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 $211.79   10.320%   $233.6467   $233.65   $233.65   $233.60  
  Purchase #2 $43.40   5.803%   $45.9185   $45.92   $45.90   $45.90  
  Purchase #3 $83.52   5.795%   $88.36   $88.36   $88.35   $88.40  
  Purchase #4 $204.42   6.211%   $217.1165   $217.12   $217.10   $217.10  
  Purchase #5 $118.39   12.226%   $132.8644   $132.86   $132.85   $132.90  
  Purchase #6 $44.93   7.446%   $48.2755   $48.28   $48.30   $48.30  
  Purchase #7 $90.63   10.540%   $100.1824   $100.18   $100.20   $100.20  
  7 purchase totals = $797.08       $866.3640   $866.37   $866.35   $866.40