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 $100.95   7.140%   $108.1578   $108.16   $108.15   $108.20  
  Purchase #2 $242.86   5.856%   $257.0819   $257.08   $257.10   $257.10  
  Purchase #3 $237.85   12.477%   $267.5265   $267.53   $267.55   $267.50  
  Purchase #4 $182.87   5.824%   $193.5203   $193.52   $193.50   $193.50  
  Purchase #5 $67.98   10.647%   $75.2178   $75.22   $75.20   $75.20  
  Purchase #6 $29.31   8.357%   $31.7594   $31.76   $31.75   $31.80  
  Purchase #7 $149.98   4.581%   $156.8506   $156.85   $156.85   $156.90  
  7 purchase totals = $1,011.80       $1,090.1143   $1,090.12   $1,090.10   $1,090.20