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 $233.32   10.829%   $258.5862   $258.59   $258.60   $258.60  
  Purchase #2 $83.34   12.757%   $93.9717   $93.97   $93.95   $94.00  
  Purchase #3 $182.59   9.372%   $199.7023   $199.70   $199.70   $199.70  
  Purchase #4 $181.88   3.612%   $188.4495   $188.45   $188.45   $188.40  
  Purchase #5 $183.49   9.807%   $201.4849   $201.48   $201.50   $201.50  
  Purchase #6 $13.55   8.185%   $14.6591   $14.66   $14.65   $14.70  
  Purchase #7 $107.78   11.107%   $119.7511   $119.75   $119.75   $119.80  
  7 purchase totals = $985.95       $1,076.6048   $1,076.60   $1,076.60   $1,076.70