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 $62.86   13.781%   $71.5227   $71.52   $71.50   $71.50  
  Purchase #2 $54.57   13.196%   $61.7711   $61.77   $61.75   $61.80  
  Purchase #3 $184.75   5.735%   $195.3454   $195.35   $195.35   $195.30  
  Purchase #4 $150.73   10.297%   $166.2507   $166.25   $166.25   $166.30  
  Purchase #5 $208.92   8.654%   $226.9999   $227.00   $227.00   $227.00  
  Purchase #6 $179.45   12.843%   $202.4968   $202.50   $202.50   $202.50  
  Purchase #7 $231.26   6.449%   $246.174   $246.17   $246.15   $246.20  
  7 purchase totals = $1,072.54       $1,170.5606   $1,170.56   $1,170.50   $1,170.60