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 $56.35   10.521%   $62.2786   $62.28   $62.30   $62.30  
  Purchase #2 $246.59   4.764%   $258.3375   $258.34   $258.35   $258.30  
  Purchase #3 $230.71   5.582%   $243.5882   $243.59   $243.60   $243.60  
  Purchase #4 $102.97   7.450%   $110.6413   $110.64   $110.65   $110.60  
  Purchase #5 $235.36   11.120%   $261.532   $261.53   $261.55   $261.50  
  Purchase #6 $21.88   9.143%   $23.8805   $23.88   $23.90   $23.90  
  Purchase #7 $160.33   10.412%   $177.0236   $177.02   $177.00   $177.00  
  7 purchase totals = $1,054.19       $1,137.2817   $1,137.28   $1,137.35   $1,137.20