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 $116.68   5.751%   $123.3903   $123.39   $123.40   $123.40  
  Purchase #2 $80.27   6.812%   $85.738   $85.74   $85.75   $85.70  
  Purchase #3 $228.89   4.417%   $239.0001   $239.00   $239.00   $239.00  
  Purchase #4 $201.59   11.671%   $225.1176   $225.12   $225.10   $225.10  
  Purchase #5 $92.93   10.799%   $102.9655   $102.97   $102.95   $103.00  
  Purchase #6 $75.72   11.132%   $84.1492   $84.15   $84.15   $84.10  
  Purchase #7 $150.64   10.371%   $166.2629   $166.26   $166.25   $166.30  
  7 purchase totals = $946.72       $1,026.6236   $1,026.63   $1,026.60   $1,026.60