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 $245.44   8.316%   $265.8508   $265.85   $265.85   $265.90  
  Purchase #2 $180.56   11.412%   $201.1655   $201.17   $201.15   $201.20  
  Purchase #3 $84.31   12.363%   $94.7332   $94.73   $94.75   $94.70  
  Purchase #4 $30.72   11.524%   $34.2602   $34.26   $34.25   $34.30  
  Purchase #5 $218.37   11.370%   $243.1987   $243.20   $243.20   $243.20  
  Purchase #6 $80.57   9.703%   $88.3877   $88.39   $88.40   $88.40  
  Purchase #7 $184.38   3.709%   $191.2187   $191.22   $191.20   $191.20  
  7 purchase totals = $1,024.35       $1,118.8148   $1,118.82   $1,118.80   $1,118.90