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 $208.71   12.322%   $234.4272   $234.43   $234.45   $234.40  
  Purchase #2 $70.54   7.372%   $75.7402   $75.74   $75.75   $75.70  
  Purchase #3 $26.96   10.656%   $29.8329   $29.83   $29.85   $29.80  
  Purchase #4 $209.42   8.782%   $227.8113   $227.81   $227.80   $227.80  
  Purchase #5 $58.59   3.139%   $60.4291   $60.43   $60.45   $60.40  
  Purchase #6 $110.88   11.684%   $123.8352   $123.84   $123.85   $123.80  
  Purchase #7 $243.35   6.323%   $258.737   $258.74   $258.75   $258.70  
  7 purchase totals = $928.45       $1,010.8129   $1,010.82   $1,010.90   $1,010.60