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 $87.84   6.565%   $93.6067   $93.61   $93.60   $93.60  
  Purchase #2 $233.94   8.363%   $253.5044   $253.50   $253.50   $253.50  
  Purchase #3 $58.46   5.837%   $61.8723   $61.87   $61.85   $61.90  
  Purchase #4 $250.74   4.789%   $262.7479   $262.75   $262.75   $262.70  
  Purchase #5 $209.84   3.659%   $217.518   $217.52   $217.50   $217.50  
  Purchase #6 $71.65   11.659%   $80.0037   $80.00   $80.00   $80.00  
  Purchase #7 $62.72   10.401%   $69.2435   $69.24   $69.25   $69.20  
  7 purchase totals = $975.19       $1,038.4965   $1,038.49   $1,038.45   $1,038.40