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 $87.59   12.634%   $98.6561   $98.66   $98.65   $98.70  
  Purchase #2 $92.61   5.408%   $97.6183   $97.62   $97.60   $97.60  
  Purchase #3 $35.50   3.832%   $36.8604   $36.86   $36.85   $36.90  
  Purchase #4 $96.60   6.759%   $103.1292   $103.13   $103.15   $103.10  
  Purchase #5 $225.64   9.474%   $247.0171   $247.02   $247.00   $247.00  
  Purchase #6 $182.57   12.748%   $205.844   $205.84   $205.85   $205.80  
  Purchase #7 $245.99   5.127%   $258.6019   $258.60   $258.60   $258.60  
  7 purchase totals = $966.50       $1,047.7270   $1,047.73   $1,047.70   $1,047.70