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 $118.57   6.230%   $125.9569   $125.96   $125.95   $126.00  
  Purchase #2 $122.49   8.745%   $133.2018   $133.20   $133.20   $133.20  
  Purchase #3 $193.52   7.389%   $207.8192   $207.82   $207.80   $207.80  
  Purchase #4 $62.29   8.632%   $67.6669   $67.67   $67.65   $67.70  
  Purchase #5 $168.65   4.113%   $175.5866   $175.59   $175.60   $175.60  
  Purchase #6 $150.62   6.296%   $160.103   $160.10   $160.10   $160.10  
  Purchase #7 $104.33   13.821%   $118.7494   $118.75   $118.75   $118.70  
  7 purchase totals = $920.47       $989.0838   $989.09   $989.05   $989.10