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 $90.85   12.562%   $102.2626   $102.26   $102.25   $102.30  
  Purchase #2 $214.86   3.802%   $223.029   $223.03   $223.05   $223.00  
  Purchase #3 $197.79   11.316%   $220.1719   $220.17   $220.15   $220.20  
  Purchase #4 $85.61   3.269%   $88.4086   $88.41   $88.40   $88.40  
  Purchase #5 $102.53   10.171%   $112.9583   $112.96   $112.95   $113.00  
  Purchase #6 $95.32   4.650%   $99.7524   $99.75   $99.75   $99.80  
  Purchase #7 $176.97   4.502%   $184.9372   $184.94   $184.95   $184.90  
  7 purchase totals = $963.93       $1,031.5200   $1,031.52   $1,031.50   $1,031.60