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 $60.55   11.853%   $67.727   $67.73   $67.75   $67.70  
  Purchase #2 $169.54   8.847%   $184.5392   $184.54   $184.55   $184.50  
  Purchase #3 $226.60   6.601%   $241.5579   $241.56   $241.55   $241.60  
  Purchase #4 $242.75   12.251%   $272.4893   $272.49   $272.50   $272.50  
  Purchase #5 $117.26   11.254%   $130.4564   $130.46   $130.45   $130.50  
  Purchase #6 $174.27   12.209%   $195.5466   $195.55   $195.55   $195.50  
  Purchase #7 $9.79   12.576%   $11.0212   $11.02   $11.00   $11.00  
  7 purchase totals = $1,000.76       $1,103.3376   $1,103.35   $1,103.35   $1,103.30