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 $157.67   10.796%   $174.6921   $174.69   $174.70   $174.70  
  Purchase #2 $118.32   11.220%   $131.5955   $131.60   $131.60   $131.60  
  Purchase #3 $118.31   5.568%   $124.8975   $124.90   $124.90   $124.90  
  Purchase #4 $62.92   3.295%   $64.9932   $64.99   $65.00   $65.00  
  Purchase #5 $167.54   8.742%   $182.1863   $182.19   $182.20   $182.20  
  Purchase #6 $163.70   9.725%   $179.6198   $179.62   $179.60   $179.60  
  Purchase #7 $206.72   10.399%   $228.2168   $228.22   $228.20   $228.20  
  7 purchase totals = $995.18       $1,086.2012   $1,086.21   $1,086.20   $1,086.20