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 $119.46   8.191%   $129.245   $129.25   $129.25   $129.20  
  Purchase #2 $236.41   4.836%   $247.8428   $247.84   $247.85   $247.80  
  Purchase #3 $227.82   9.744%   $250.0188   $250.02   $250.00   $250.00  
  Purchase #4 $214.34   8.396%   $232.336   $232.34   $232.35   $232.30  
  Purchase #5 $230.41   6.260%   $244.8337   $244.83   $244.85   $244.80  
  Purchase #6 $199.55   6.146%   $211.8143   $211.81   $211.80   $211.80  
  Purchase #7 $35.92   10.818%   $39.8058   $39.81   $39.80   $39.80  
  7 purchase totals = $1,263.91       $1,355.8964   $1,355.90   $1,355.90   $1,355.70