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 $84.54   8.846%   $92.0184   $92.02   $92.00   $92.00  
  Purchase #2 $51.98   13.424%   $58.9578   $58.96   $58.95   $59.00  
  Purchase #3 $42.32   3.642%   $43.8613   $43.86   $43.85   $43.90  
  Purchase #4 $138.53   9.755%   $152.0436   $152.04   $152.05   $152.00  
  Purchase #5 $131.60   7.640%   $141.6542   $141.65   $141.65   $141.70  
  Purchase #6 $197.30   9.252%   $215.5542   $215.55   $215.55   $215.60  
  Purchase #7 $49.96   6.492%   $53.2034   $53.20   $53.20   $53.20  
  7 purchase totals = $696.23       $757.2929   $757.28   $757.25   $757.40