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 $67.44   12.148%   $75.6326   $75.63   $75.65   $75.60  
  Purchase #2 $46.57   8.614%   $50.5815   $50.58   $50.60   $50.60  
  Purchase #3 $169.96   4.537%   $177.6711   $177.67   $177.65   $177.70  
  Purchase #4 $164.85   9.185%   $179.9915   $179.99   $180.00   $180.00  
  Purchase #5 $87.27   10.835%   $96.7257   $96.73   $96.75   $96.70  
  Purchase #6 $236.33   9.599%   $259.0153   $259.02   $259.00   $259.00  
  Purchase #7 $247.45   11.289%   $275.3846   $275.38   $275.40   $275.40  
  7 purchase totals = $1,019.87       $1,115.0023   $1,115.00   $1,115.05   $1,115.00