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 $198.91   6.523%   $211.8849   $211.88   $211.90   $211.90  
  Purchase #2 $200.93   8.642%   $218.2944   $218.29   $218.30   $218.30  
  Purchase #3 $169.79   4.802%   $177.9433   $177.94   $177.95   $177.90  
  Purchase #4 $76.90   7.759%   $82.8667   $82.87   $82.85   $82.90  
  Purchase #5 $145.36   7.331%   $156.0163   $156.02   $156.00   $156.00  
  Purchase #6 $136.71   7.431%   $146.8689   $146.87   $146.85   $146.90  
  Purchase #7 $26.35   5.470%   $27.7913   $27.79   $27.80   $27.80  
  7 purchase totals = $954.95       $1,021.6658   $1,021.66   $1,021.65   $1,021.70