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 $61.90   11.791%   $69.1986   $69.20   $69.20   $69.20  
  Purchase #2 $132.31   5.764%   $139.9363   $139.94   $139.95   $139.90  
  Purchase #3 $19.98   13.722%   $22.7217   $22.72   $22.70   $22.70  
  Purchase #4 $80.97   3.142%   $83.5141   $83.51   $83.50   $83.50  
  Purchase #5 $158.34   5.661%   $167.3036   $167.30   $167.30   $167.30  
  Purchase #6 $180.45   3.713%   $187.1501   $187.15   $187.15   $187.20  
  Purchase #7 $74.79   7.564%   $80.4471   $80.45   $80.45   $80.40  
  7 purchase totals = $708.74       $750.2715   $750.27   $750.25   $750.20