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 $184.35   8.487%   $199.9958   $200.00   $200.00   $200.00  
  Purchase #2 $50.53   7.553%   $54.3465   $54.35   $54.35   $54.30  
  Purchase #3 $185.37   9.172%   $202.3721   $202.37   $202.35   $202.40  
  Purchase #4 $247.44   9.842%   $271.793   $271.79   $271.80   $271.80  
  Purchase #5 $244.90   6.494%   $260.8038   $260.80   $260.80   $260.80  
  Purchase #6 $198.35   9.359%   $216.9136   $216.91   $216.90   $216.90  
  Purchase #7 $166.47   13.179%   $188.4091   $188.41   $188.40   $188.40  
  7 purchase totals = $1,277.41       $1,394.6339   $1,394.63   $1,394.60   $1,394.60