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 $81.96   3.207%   $84.5885   $84.59   $84.60   $84.60  
  Purchase #2 $217.67   13.287%   $246.5918   $246.59   $246.60   $246.60  
  Purchase #3 $167.38   7.322%   $179.6356   $179.64   $179.65   $179.60  
  Purchase #4 $95.97   12.436%   $107.9048   $107.90   $107.90   $107.90  
  Purchase #5 $214.35   5.144%   $225.3762   $225.38   $225.40   $225.40  
  Purchase #6 $200.99   7.392%   $215.8472   $215.85   $215.85   $215.80  
  Purchase #7 $142.91   8.821%   $155.5161   $155.52   $155.50   $155.50  
  7 purchase totals = $1,121.23       $1,215.4602   $1,215.47   $1,215.50   $1,215.40