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 $117.40   12.695%   $132.3039   $132.30   $132.30   $132.30  
  Purchase #2 $116.30   4.766%   $121.8429   $121.84   $121.85   $121.80  
  Purchase #3 $45.64   4.120%   $47.5204   $47.52   $47.50   $47.50  
  Purchase #4 $243.25   10.381%   $268.5018   $268.50   $268.50   $268.50  
  Purchase #5 $204.39   10.813%   $226.4907   $226.49   $226.50   $226.50  
  Purchase #6 $55.60   4.449%   $58.0736   $58.07   $58.05   $58.10  
  Purchase #7 $148.90   4.430%   $155.4963   $155.50   $155.50   $155.50  
  7 purchase totals = $931.48       $1,010.2296   $1,010.22   $1,010.20   $1,010.20