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 $226.64   10.129%   $249.5964   $249.60   $249.60   $249.60  
  Purchase #2 $239.89   13.716%   $272.7933   $272.79   $272.80   $272.80  
  Purchase #3 $147.91   4.107%   $153.9847   $153.98   $154.00   $154.00  
  Purchase #4 $110.85   12.473%   $124.6763   $124.68   $124.70   $124.70  
  Purchase #5 $237.32   11.798%   $265.319   $265.32   $265.30   $265.30  
  Purchase #6 $222.98   4.754%   $233.5805   $233.58   $233.60   $233.60  
  Purchase #7 $70.27   6.775%   $75.0308   $75.03   $75.05   $75.00  
  7 purchase totals = $1,255.86       $1,374.9810   $1,374.98   $1,375.05   $1,375.00