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 $227.95   11.720%   $254.6657   $254.67   $254.65   $254.70  
  Purchase #2 $220.98   12.207%   $247.955   $247.96   $247.95   $248.00  
  Purchase #3 $73.37   11.698%   $81.9528   $81.95   $81.95   $82.00  
  Purchase #4 $164.52   10.227%   $181.3455   $181.35   $181.35   $181.30  
  Purchase #5 $250.74   13.768%   $285.2619   $285.26   $285.25   $285.30  
  Purchase #6 $111.46   12.499%   $125.3914   $125.39   $125.40   $125.40  
  Purchase #7 $192.36   3.333%   $198.7714   $198.77   $198.75   $198.80  
  7 purchase totals = $1,241.38       $1,375.3437   $1,375.35   $1,375.30   $1,375.50