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 $61.91   12.147%   $69.4302   $69.43   $69.45   $69.40  
  Purchase #2 $106.93   9.525%   $117.1151   $117.12   $117.10   $117.10  
  Purchase #3 $194.40   4.426%   $203.0041   $203.00   $203.00   $203.00  
  Purchase #4 $135.87   7.470%   $146.0195   $146.02   $146.00   $146.00  
  Purchase #5 $46.62   8.133%   $50.4116   $50.41   $50.40   $50.40  
  Purchase #6 $61.64   7.566%   $66.3037   $66.30   $66.30   $66.30  
  Purchase #7 $99.48   11.374%   $110.7949   $110.79   $110.80   $110.80  
  7 purchase totals = $706.85       $763.0791   $763.07   $763.05   $763.00