Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $110.52   5.824%   $116.9567   $116.96   $116.95   $117.00  
  Purchase #2 $93.67   10.194%   $103.2187   $103.22   $103.20   $103.20  
  Purchase #3 $212.66   12.597%   $239.4488   $239.45   $239.45   $239.40  
  Purchase #4 $150.61   9.772%   $165.3276   $165.33   $165.35   $165.30  
  Purchase #5 $218.28   3.710%   $226.3782   $226.38   $226.40   $226.40  
  Purchase #6 $160.30   13.505%   $181.9485   $181.95   $181.95   $181.90  
  Purchase #7 $119.29   5.802%   $126.2112   $126.21   $126.20   $126.20  
  7 purchase totals = $1,065.33       $1,159.4897   $1,159.50   $1,159.50   $1,159.40