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 $96.52   12.456%   $108.5425   $108.54   $108.55   $108.50  
  Purchase #2 $217.34   13.663%   $247.0352   $247.04   $247.05   $247.00  
  Purchase #3 $118.26   8.315%   $128.0933   $128.09   $128.10   $128.10  
  Purchase #4 $230.72   5.697%   $243.8641   $243.86   $243.85   $243.90  
  Purchase #5 $162.63   12.310%   $182.6498   $182.65   $182.65   $182.60  
  Purchase #6 $233.41   5.244%   $245.65   $245.65   $245.65   $245.70  
  Purchase #7 $246.93   8.126%   $266.9955   $267.00   $267.00   $267.00  
  7 purchase totals = $1,305.81       $1,422.8304   $1,422.83   $1,422.85   $1,422.80