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 $188.58   12.208%   $211.6018   $211.60   $211.60   $211.60  
  Purchase #2 $31.64   11.780%   $35.3672   $35.37   $35.35   $35.40  
  Purchase #3 $127.97   10.754%   $141.7319   $141.73   $141.75   $141.70  
  Purchase #4 $58.78   8.170%   $63.5823   $63.58   $63.60   $63.60  
  Purchase #5 $110.35   5.361%   $116.2659   $116.27   $116.25   $116.30  
  Purchase #6 $177.90   7.816%   $191.8047   $191.80   $191.80   $191.80  
  Purchase #7 $213.92   12.367%   $240.3755   $240.38   $240.40   $240.40  
  7 purchase totals = $909.14       $1,000.7293   $1,000.73   $1,000.75   $1,000.80