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 $55.87   12.867%   $63.0588   $63.06   $63.05   $63.10  
  Purchase #2 $227.94   4.780%   $238.8355   $238.84   $238.85   $238.80  
  Purchase #3 $186.94   8.118%   $202.1158   $202.12   $202.10   $202.10  
  Purchase #4 $206.25   12.863%   $232.7799   $232.78   $232.80   $232.80  
  Purchase #5 $173.94   7.709%   $187.349   $187.35   $187.35   $187.30  
  Purchase #6 $158.89   6.382%   $169.0304   $169.03   $169.05   $169.00  
  Purchase #7 $222.48   11.582%   $248.2476   $248.25   $248.25   $248.20  
  7 purchase totals = $1,232.31       $1,341.4170   $1,341.43   $1,341.45   $1,341.30