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 $65.25   13.646%   $74.154   $74.15   $74.15   $74.20  
  Purchase #2 $88.85   4.628%   $92.962   $92.96   $92.95   $93.00  
  Purchase #3 $75.88   8.541%   $82.3609   $82.36   $82.35   $82.40  
  Purchase #4 $66.88   5.637%   $70.65   $70.65   $70.65   $70.70  
  Purchase #5 $187.98   6.175%   $199.5878   $199.59   $199.60   $199.60  
  Purchase #6 $219.89   8.268%   $238.0705   $238.07   $238.05   $238.10  
  Purchase #7 $8.32   11.461%   $9.2736   $9.27   $9.25   $9.30  
  7 purchase totals = $713.05       $767.0588   $767.05   $767.00   $767.30