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 $245.41   9.696%   $269.205   $269.21   $269.20   $269.20  
  Purchase #2 $21.68   3.650%   $22.4713   $22.47   $22.45   $22.50  
  Purchase #3 $51.58   13.765%   $58.68   $58.68   $58.70   $58.70  
  Purchase #4 $62.80   6.705%   $67.0107   $67.01   $67.00   $67.00  
  Purchase #5 $203.93   8.259%   $220.7726   $220.77   $220.75   $220.80  
  Purchase #6 $163.84   12.707%   $184.6591   $184.66   $184.65   $184.70  
  Purchase #7 $95.46   8.240%   $103.3259   $103.33   $103.35   $103.30  
  7 purchase totals = $844.70       $926.1246   $926.13   $926.10   $926.20