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 $68.99   8.708%   $74.9976   $75.00   $75.00   $75.00  
  Purchase #2 $238.73   8.767%   $259.6595   $259.66   $259.65   $259.70  
  Purchase #3 $211.79   4.782%   $221.9178   $221.92   $221.90   $221.90  
  Purchase #4 $165.90   7.640%   $178.5748   $178.57   $178.55   $178.60  
  Purchase #5 $67.73   9.449%   $74.1298   $74.13   $74.15   $74.10  
  Purchase #6 $98.28   6.802%   $104.965   $104.97   $104.95   $105.00  
  Purchase #7 $54.48   3.282%   $56.268   $56.27   $56.25   $56.30  
  7 purchase totals = $905.90       $970.5125   $970.52   $970.45   $970.60