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 $114.78   3.270%   $118.5333   $118.53   $118.55   $118.50  
  Purchase #2 $50.97   3.207%   $52.6046   $52.60   $52.60   $52.60  
  Purchase #3 $192.91   8.123%   $208.5801   $208.58   $208.60   $208.60  
  Purchase #4 $178.32   6.432%   $189.7895   $189.79   $189.80   $189.80  
  Purchase #5 $61.91   10.197%   $68.223   $68.22   $68.20   $68.20  
  Purchase #6 $219.60   11.555%   $244.9748   $244.97   $244.95   $245.00  
  Purchase #7 $62.89   4.607%   $65.7873   $65.79   $65.80   $65.80  
  7 purchase totals = $881.38       $948.4926   $948.48   $948.50   $948.50