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 $106.89   11.792%   $119.4945   $119.49   $119.50   $119.50  
  Purchase #2 $108.60   11.312%   $120.8848   $120.88   $120.90   $120.90  
  Purchase #3 $62.54   3.365%   $64.6445   $64.64   $64.65   $64.60  
  Purchase #4 $243.42   5.587%   $257.0199   $257.02   $257.00   $257.00  
  Purchase #5 $50.94   13.428%   $57.7802   $57.78   $57.80   $57.80  
  Purchase #6 $154.95   9.623%   $169.8608   $169.86   $169.85   $169.90  
  Purchase #7 $232.52   6.149%   $246.8177   $246.82   $246.80   $246.80  
  7 purchase totals = $959.86       $1,036.5024   $1,036.49   $1,036.50   $1,036.50