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 $177.38   13.297%   $200.9662   $200.97   $200.95   $201.00  
  Purchase #2 $19.36   13.694%   $22.0112   $22.01   $22.00   $22.00  
  Purchase #3 $120.80   6.751%   $128.9552   $128.96   $128.95   $129.00  
  Purchase #4 $27.67   9.310%   $30.2461   $30.25   $30.25   $30.20  
  Purchase #5 $217.82   12.751%   $245.5942   $245.59   $245.60   $245.60  
  Purchase #6 $58.83   9.870%   $64.6365   $64.64   $64.65   $64.60  
  Purchase #7 $129.78   3.413%   $134.2094   $134.21   $134.20   $134.20  
  7 purchase totals = $751.64       $826.6188   $826.63   $826.60   $826.60