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 $198.96   13.718%   $226.2533   $226.25   $226.25   $226.30  
  Purchase #2 $10.89   5.761%   $11.5174   $11.52   $11.50   $11.50  
  Purchase #3 $43.57   5.869%   $46.1271   $46.13   $46.15   $46.10  
  Purchase #4 $10.49   9.594%   $11.4964   $11.50   $11.50   $11.50  
  Purchase #5 $203.68   6.592%   $217.1066   $217.11   $217.10   $217.10  
  Purchase #6 $246.62   8.684%   $268.0365   $268.04   $268.05   $268.00  
  Purchase #7 $151.75   5.173%   $159.6   $159.60   $159.60   $159.60  
  7 purchase totals = $865.96       $940.1373   $940.15   $940.15   $940.10