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 $208.66   12.756%   $235.2767   $235.28   $235.30   $235.30  
  Purchase #2 $161.39   8.333%   $174.8386   $174.84   $174.85   $174.80  
  Purchase #3 $220.72   10.401%   $243.6771   $243.68   $243.70   $243.70  
  Purchase #4 $59.47   9.355%   $65.0334   $65.03   $65.05   $65.00  
  Purchase #5 $12.27   5.270%   $12.9166   $12.92   $12.90   $12.90  
  Purchase #6 $25.97   13.317%   $29.4284   $29.43   $29.45   $29.40  
  Purchase #7 $136.71   13.642%   $155.36   $155.36   $155.35   $155.40  
  7 purchase totals = $825.19       $916.5308   $916.54   $916.60   $916.50