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 $232.86   9.490%   $254.9584   $254.96   $254.95   $255.00  
  Purchase #2 $160.85   13.374%   $182.3621   $182.36   $182.35   $182.40  
  Purchase #3 $37.52   10.830%   $41.5834   $41.58   $41.60   $41.60  
  Purchase #4 $59.64   12.717%   $67.2244   $67.22   $67.20   $67.20  
  Purchase #5 $248.66   10.582%   $274.9732   $274.97   $274.95   $275.00  
  Purchase #6 $180.48   3.527%   $186.8455   $186.85   $186.85   $186.80  
  Purchase #7 $103.52   13.315%   $117.3037   $117.30   $117.30   $117.30  
  7 purchase totals = $1,023.53       $1,125.2507   $1,125.24   $1,125.20   $1,125.30