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 $195.93   10.620%   $216.7378   $216.74   $216.75   $216.70  
  Purchase #2 $101.96   12.528%   $114.7335   $114.73   $114.75   $114.70  
  Purchase #3 $87.98   7.524%   $94.5996   $94.60   $94.60   $94.60  
  Purchase #4 $85.52   3.855%   $88.8168   $88.82   $88.80   $88.80  
  Purchase #5 $200.64   8.595%   $217.885   $217.89   $217.90   $217.90  
  Purchase #6 $152.46   11.788%   $170.432   $170.43   $170.45   $170.40  
  Purchase #7 $158.69   13.131%   $179.5276   $179.53   $179.55   $179.50  
  7 purchase totals = $983.18       $1,082.7323   $1,082.74   $1,082.80   $1,082.60