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 $81.81   3.612%   $84.765   $84.77   $84.75   $84.80  
  Purchase #2 $195.43   4.486%   $204.197   $204.20   $204.20   $204.20  
  Purchase #3 $88.94   13.510%   $100.9558   $100.96   $100.95   $101.00  
  Purchase #4 $152.44   13.562%   $173.1139   $173.11   $173.10   $173.10  
  Purchase #5 $91.98   4.562%   $96.1761   $96.18   $96.20   $96.20  
  Purchase #6 $167.79   9.166%   $183.1696   $183.17   $183.15   $183.20  
  Purchase #7 $199.25   8.168%   $215.5247   $215.52   $215.50   $215.50  
  7 purchase totals = $977.64       $1,057.9021   $1,057.91   $1,057.85   $1,058.00