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 $91.58   3.205%   $94.5151   $94.52   $94.50   $94.50  
  Purchase #2 $51.37   6.622%   $54.7717   $54.77   $54.75   $54.80  
  Purchase #3 $125.46   6.507%   $133.6237   $133.62   $133.60   $133.60  
  Purchase #4 $211.96   13.581%   $240.7463   $240.75   $240.75   $240.70  
  Purchase #5 $189.74   6.585%   $202.2344   $202.23   $202.25   $202.20  
  Purchase #6 $74.52   13.705%   $84.733   $84.73   $84.75   $84.70  
  Purchase #7 $66.74   12.595%   $75.1459   $75.15   $75.15   $75.10  
  7 purchase totals = $811.37       $885.7701   $885.77   $885.75   $885.60