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 $245.49   12.617%   $276.4635   $276.46   $276.45   $276.50  
  Purchase #2 $77.58   9.561%   $84.9974   $85.00   $85.00   $85.00  
  Purchase #3 $95.30   10.388%   $105.1998   $105.20   $105.20   $105.20  
  Purchase #4 $162.66   4.471%   $169.9325   $169.93   $169.95   $169.90  
  Purchase #5 $194.39   5.142%   $204.3855   $204.39   $204.40   $204.40  
  Purchase #6 $34.44   8.380%   $37.3261   $37.33   $37.35   $37.30  
  Purchase #7 $127.29   4.292%   $132.7533   $132.75   $132.75   $132.80  
  7 purchase totals = $937.15       $1,011.0581   $1,011.06   $1,011.10   $1,011.10