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 $184.79   11.331%   $205.7286   $205.73   $205.75   $205.70  
  Purchase #2 $67.86   13.208%   $76.8229   $76.82   $76.80   $76.80  
  Purchase #3 $53.45   9.692%   $58.6304   $58.63   $58.65   $58.60  
  Purchase #4 $205.49   13.271%   $232.7606   $232.76   $232.75   $232.80  
  Purchase #5 $246.85   8.350%   $267.462   $267.46   $267.45   $267.50  
  Purchase #6 $130.73   9.132%   $142.6683   $142.67   $142.65   $142.70  
  Purchase #7 $53.39   7.571%   $57.4322   $57.43   $57.45   $57.40  
  7 purchase totals = $942.56       $1,041.5050   $1,041.50   $1,041.50   $1,041.50