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 $211.57   12.354%   $237.7074   $237.71   $237.70   $237.70  
  Purchase #2 $110.85   10.515%   $122.5059   $122.51   $122.50   $122.50  
  Purchase #3 $227.84   4.147%   $237.2885   $237.29   $237.30   $237.30  
  Purchase #4 $81.32   5.734%   $85.9829   $85.98   $86.00   $86.00  
  Purchase #5 $141.45   13.230%   $160.1638   $160.16   $160.15   $160.20  
  Purchase #6 $134.42   8.860%   $146.3296   $146.33   $146.35   $146.30  
  Purchase #7 $60.64   6.512%   $64.5889   $64.59   $64.60   $64.60  
  7 purchase totals = $968.09       $1,054.5670   $1,054.57   $1,054.60   $1,054.60