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 $240.40   9.551%   $263.3606   $263.36   $263.35   $263.40  
  Purchase #2 $117.79   6.669%   $125.6454   $125.65   $125.65   $125.60  
  Purchase #3 $241.37   11.767%   $269.772   $269.77   $269.75   $269.80  
  Purchase #4 $103.55   5.114%   $108.8455   $108.85   $108.85   $108.80  
  Purchase #5 $202.93   3.761%   $210.5622   $210.56   $210.55   $210.60  
  Purchase #6 $239.72   4.562%   $250.656   $250.66   $250.65   $250.70  
  Purchase #7 $13.52   4.698%   $14.1552   $14.16   $14.15   $14.20  
  7 purchase totals = $1,159.28       $1,242.9969   $1,243.01   $1,242.95   $1,243.10