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 $206.93   3.694%   $214.574   $214.57   $214.55   $214.60  
  Purchase #2 $52.97   12.302%   $59.4864   $59.49   $59.50   $59.50  
  Purchase #3 $109.97   9.328%   $120.228   $120.23   $120.25   $120.20  
  Purchase #4 $95.84   8.435%   $103.9241   $103.92   $103.90   $103.90  
  Purchase #5 $215.98   8.323%   $233.956   $233.96   $233.95   $234.00  
  Purchase #6 $128.89   6.216%   $136.9018   $136.90   $136.90   $136.90  
  Purchase #7 $189.68   13.572%   $215.4234   $215.42   $215.40   $215.40  
  7 purchase totals = $1,000.26       $1,084.4937   $1,084.49   $1,084.45   $1,084.50