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 $59.97   4.653%   $62.7604   $62.76   $62.75   $62.80  
  Purchase #2 $160.93   8.731%   $174.9808   $174.98   $175.00   $175.00  
  Purchase #3 $235.85   9.805%   $258.9751   $258.98   $259.00   $259.00  
  Purchase #4 $172.65   6.346%   $183.6064   $183.61   $183.60   $183.60  
  Purchase #5 $167.49   9.497%   $183.3965   $183.40   $183.40   $183.40  
  Purchase #6 $19.46   12.113%   $21.8172   $21.82   $21.80   $21.80  
  Purchase #7 $117.42   10.520%   $129.7726   $129.77   $129.75   $129.80  
  7 purchase totals = $933.77       $1,015.3090   $1,015.32   $1,015.30   $1,015.40