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 $166.47   8.142%   $180.024   $180.02   $180.00   $180.00  
  Purchase #2 $226.53   13.302%   $256.663   $256.66   $256.65   $256.70  
  Purchase #3 $35.86   8.139%   $38.7786   $38.78   $38.80   $38.80  
  Purchase #4 $132.55   4.607%   $138.6566   $138.66   $138.65   $138.70  
  Purchase #5 $159.95   11.221%   $177.898   $177.90   $177.90   $177.90  
  Purchase #6 $137.39   9.375%   $150.2703   $150.27   $150.25   $150.30  
  Purchase #7 $152.53   7.667%   $164.2245   $164.22   $164.20   $164.20  
  7 purchase totals = $1,011.28       $1,106.5150   $1,106.51   $1,106.45   $1,106.60