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 $58.80   6.418%   $62.5738   $62.57   $62.55   $62.60  
  Purchase #2 $247.56   8.112%   $267.6421   $267.64   $267.65   $267.60  
  Purchase #3 $82.63   7.676%   $88.9727   $88.97   $88.95   $89.00  
  Purchase #4 $36.40   11.477%   $40.5776   $40.58   $40.60   $40.60  
  Purchase #5 $248.90   13.195%   $281.7424   $281.74   $281.75   $281.70  
  Purchase #6 $113.97   11.458%   $127.0287   $127.03   $127.05   $127.00  
  Purchase #7 $195.49   13.343%   $221.5742   $221.57   $221.55   $221.60  
  7 purchase totals = $983.75       $1,090.1115   $1,090.10   $1,090.10   $1,090.10