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 $232.50   9.662%   $254.9642   $254.96   $254.95   $255.00  
  Purchase #2 $146.64   6.861%   $156.701   $156.70   $156.70   $156.70  
  Purchase #3 $119.58   5.712%   $126.4104   $126.41   $126.40   $126.40  
  Purchase #4 $111.96   12.131%   $125.5419   $125.54   $125.55   $125.50  
  Purchase #5 $107.67   10.761%   $119.2564   $119.26   $119.25   $119.30  
  Purchase #6 $59.97   12.272%   $67.3295   $67.33   $67.35   $67.30  
  Purchase #7 $38.84   12.362%   $43.6414   $43.64   $43.65   $43.60  
  7 purchase totals = $817.16       $893.8448   $893.84   $893.85   $893.80