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 $232.85   9.327%   $254.5679   $254.57   $254.55   $254.60  
  Purchase #2 $75.68   10.587%   $83.6922   $83.69   $83.70   $83.70  
  Purchase #3 $20.43   10.245%   $22.5231   $22.52   $22.50   $22.50  
  Purchase #4 $55.26   7.327%   $59.3089   $59.31   $59.30   $59.30  
  Purchase #5 $86.46   7.573%   $93.0076   $93.01   $93.00   $93.00  
  Purchase #6 $117.38   7.797%   $126.5321   $126.53   $126.55   $126.50  
  Purchase #7 $210.71   11.587%   $235.125   $235.13   $235.15   $235.10  
  7 purchase totals = $798.77       $874.7568   $874.76   $874.75   $874.70