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 $66.70   3.468%   $69.0132   $69.01   $69.00   $69.00  
  Purchase #2 $30.79   13.663%   $34.9968   $35.00   $35.00   $35.00  
  Purchase #3 $99.52   13.489%   $112.9443   $112.94   $112.95   $112.90  
  Purchase #4 $16.74   4.767%   $17.538   $17.54   $17.55   $17.50  
  Purchase #5 $90.82   5.635%   $95.9377   $95.94   $95.95   $95.90  
  Purchase #6 $58.35   4.482%   $60.9652   $60.97   $60.95   $61.00  
  Purchase #7 $53.29   11.516%   $59.4269   $59.43   $59.45   $59.40  
  7 purchase totals = $416.21       $450.8221   $450.83   $450.85   $450.70