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 $190.56   6.459%   $202.8683   $202.87   $202.85   $202.90  
  Purchase #2 $164.41   5.457%   $173.3819   $173.38   $173.40   $173.40  
  Purchase #3 $47.81   6.417%   $50.878   $50.88   $50.90   $50.90  
  Purchase #4 $116.88   7.751%   $125.9394   $125.94   $125.95   $125.90  
  Purchase #5 $166.76   12.339%   $187.3365   $187.34   $187.35   $187.30  
  Purchase #6 $171.75   10.414%   $189.636   $189.64   $189.65   $189.60  
  Purchase #7 $90.82   6.184%   $96.4363   $96.44   $96.45   $96.40  
  7 purchase totals = $948.99       $1,026.4764   $1,026.49   $1,026.55   $1,026.40