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 $65.46   11.848%   $73.2157   $73.22   $73.20   $73.20  
  Purchase #2 $95.49   12.194%   $107.1341   $107.13   $107.15   $107.10  
  Purchase #3 $243.57   10.432%   $268.9792   $268.98   $269.00   $269.00  
  Purchase #4 $205.82   9.657%   $225.696   $225.70   $225.70   $225.70  
  Purchase #5 $136.67   4.335%   $142.5946   $142.59   $142.60   $142.60  
  Purchase #6 $141.40   13.513%   $160.5074   $160.51   $160.50   $160.50  
  Purchase #7 $229.98   9.225%   $251.1957   $251.20   $251.20   $251.20  
  7 purchase totals = $1,118.39       $1,229.3227   $1,229.33   $1,229.35   $1,229.30