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 $53.98   11.444%   $60.1575   $60.16   $60.15   $60.20  
  Purchase #2 $163.88   10.391%   $180.9088   $180.91   $180.90   $180.90  
  Purchase #3 $143.86   3.254%   $148.5412   $148.54   $148.55   $148.50  
  Purchase #4 $235.95   11.679%   $263.5066   $263.51   $263.50   $263.50  
  Purchase #5 $172.45   12.840%   $194.5926   $194.59   $194.60   $194.60  
  Purchase #6 $7.86   6.538%   $8.3739   $8.37   $8.35   $8.40  
  Purchase #7 $152.29   7.271%   $163.363   $163.36   $163.35   $163.40  
  7 purchase totals = $930.27       $1,019.4436   $1,019.44   $1,019.40   $1,019.50