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 $59.54   11.424%   $66.3418   $66.34   $66.35   $66.30  
  Purchase #2 $230.73   5.294%   $242.9448   $242.94   $242.95   $242.90  
  Purchase #3 $84.92   7.738%   $91.4911   $91.49   $91.50   $91.50  
  Purchase #4 $203.50   9.808%   $223.4593   $223.46   $223.45   $223.50  
  Purchase #5 $150.49   10.288%   $165.9724   $165.97   $165.95   $166.00  
  Purchase #6 $233.61   3.403%   $241.5597   $241.56   $241.55   $241.60  
  Purchase #7 $150.81   6.256%   $160.2447   $160.24   $160.25   $160.20  
  7 purchase totals = $1,113.60       $1,192.0138   $1,192.00   $1,192.00   $1,192.00