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 $102.59   4.316%   $107.0178   $107.02   $107.00   $107.00  
  Purchase #2 $62.96   10.587%   $69.6256   $69.63   $69.65   $69.60  
  Purchase #3 $91.74   5.258%   $96.5637   $96.56   $96.55   $96.60  
  Purchase #4 $151.79   10.616%   $167.904   $167.90   $167.90   $167.90  
  Purchase #5 $87.28   6.150%   $92.6477   $92.65   $92.65   $92.60  
  Purchase #6 $227.85   5.805%   $241.0767   $241.08   $241.10   $241.10  
  Purchase #7 $68.71   4.376%   $71.7167   $71.72   $71.70   $71.70  
  7 purchase totals = $792.92       $846.5522   $846.56   $846.55   $846.50