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 $63.96   8.371%   $69.3141   $69.31   $69.30   $69.30  
  Purchase #2 $131.45   13.156%   $148.7436   $148.74   $148.75   $148.70  
  Purchase #3 $89.84   3.273%   $92.7805   $92.78   $92.80   $92.80  
  Purchase #4 $203.56   13.170%   $230.3689   $230.37   $230.35   $230.40  
  Purchase #5 $226.40   13.450%   $256.8508   $256.85   $256.85   $256.90  
  Purchase #6 $179.26   8.757%   $194.9578   $194.96   $194.95   $195.00  
  Purchase #7 $28.37   6.104%   $30.1017   $30.10   $30.10   $30.10  
  7 purchase totals = $922.84       $1,023.1174   $1,023.11   $1,023.10   $1,023.20