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 $67.81   5.628%   $71.6263   $71.63   $71.65   $71.60  
  Purchase #2 $150.75   6.778%   $160.9678   $160.97   $160.95   $161.00  
  Purchase #3 $31.45   6.675%   $33.5493   $33.55   $33.55   $33.50  
  Purchase #4 $148.74   4.819%   $155.9078   $155.91   $155.90   $155.90  
  Purchase #5 $227.43   9.366%   $248.7311   $248.73   $248.75   $248.70  
  Purchase #6 $84.98   12.205%   $95.3518   $95.35   $95.35   $95.40  
  Purchase #7 $160.73   6.812%   $171.6789   $171.68   $171.70   $171.70  
  7 purchase totals = $871.89       $937.8130   $937.82   $937.85   $937.80