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 $183.29   6.259%   $194.7621   $194.76   $194.75   $194.80  
  Purchase #2 $233.96   12.614%   $263.4717   $263.47   $263.45   $263.50  
  Purchase #3 $21.78   11.205%   $24.2204   $24.22   $24.20   $24.20  
  Purchase #4 $31.72   3.698%   $32.893   $32.89   $32.90   $32.90  
  Purchase #5 $115.70   13.831%   $131.7025   $131.70   $131.70   $131.70  
  Purchase #6 $91.60   4.552%   $95.7696   $95.77   $95.75   $95.80  
  Purchase #7 $173.37   6.244%   $184.1952   $184.20   $184.20   $184.20  
  7 purchase totals = $851.42       $927.0145   $927.01   $926.95   $927.10