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 $60.80   5.273%   $64.006   $64.01   $64.00   $64.00  
  Purchase #2 $226.93   3.795%   $235.542   $235.54   $235.55   $235.50  
  Purchase #3 $116.64   6.448%   $124.1609   $124.16   $124.15   $124.20  
  Purchase #4 $58.44   11.414%   $65.1103   $65.11   $65.10   $65.10  
  Purchase #5 $106.86   3.818%   $110.9399   $110.94   $110.95   $110.90  
  Purchase #6 $41.79   4.392%   $43.6254   $43.63   $43.65   $43.60  
  Purchase #7 $9.90   8.174%   $10.7092   $10.71   $10.70   $10.70  
  7 purchase totals = $621.36       $654.0937   $654.10   $654.10   $654.00