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 $63.78   8.123%   $68.9608   $68.96   $68.95   $69.00  
  Purchase #2 $88.74   12.528%   $99.8573   $99.86   $99.85   $99.90  
  Purchase #3 $25.38   13.703%   $28.8578   $28.86   $28.85   $28.90  
  Purchase #4 $120.61   3.705%   $125.0786   $125.08   $125.10   $125.10  
  Purchase #5 $107.40   10.685%   $118.8757   $118.88   $118.90   $118.90  
  Purchase #6 $143.96   3.312%   $148.728   $148.73   $148.75   $148.70  
  Purchase #7 $211.90   5.547%   $223.6541   $223.65   $223.65   $223.70  
  7 purchase totals = $761.77       $814.0123   $814.02   $814.05   $814.20