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 $55.84   11.168%   $62.0762   $62.08   $62.10   $62.10  
  Purchase #2 $25.52   8.157%   $27.6017   $27.60   $27.60   $27.60  
  Purchase #3 $215.98   13.138%   $244.3555   $244.36   $244.35   $244.40  
  Purchase #4 $122.44   13.737%   $139.2596   $139.26   $139.25   $139.30  
  Purchase #5 $232.66   9.713%   $255.2583   $255.26   $255.25   $255.30  
  Purchase #6 $160.71   6.800%   $171.6383   $171.64   $171.65   $171.60  
  Purchase #7 $152.87   3.686%   $158.5048   $158.50   $158.50   $158.50  
  7 purchase totals = $966.02       $1,058.6944   $1,058.70   $1,058.70   $1,058.80