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 $196.84   13.717%   $223.8405   $223.84   $223.85   $223.80  
  Purchase #2 $223.77   10.385%   $247.0085   $247.01   $247.00   $247.00  
  Purchase #3 $243.74   7.644%   $262.3715   $262.37   $262.35   $262.40  
  Purchase #4 $65.54   3.132%   $67.5927   $67.59   $67.60   $67.60  
  Purchase #5 $6.30   6.823%   $6.7298   $6.73   $6.75   $6.70  
  Purchase #6 $220.28   9.129%   $240.3894   $240.39   $240.40   $240.40  
  Purchase #7 $246.43   4.277%   $256.9698   $256.97   $256.95   $257.00  
  7 purchase totals = $1,202.90       $1,304.9022   $1,304.90   $1,304.90   $1,304.90