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 $63.75   12.703%   $71.8482   $71.85   $71.85   $71.80  
  Purchase #2 $246.54   9.191%   $269.1995   $269.20   $269.20   $269.20  
  Purchase #3 $184.38   12.121%   $206.7287   $206.73   $206.75   $206.70  
  Purchase #4 $169.92   4.489%   $177.5477   $177.55   $177.55   $177.50  
  Purchase #5 $102.95   8.546%   $111.7481   $111.75   $111.75   $111.70  
  Purchase #6 $147.98   3.215%   $152.7376   $152.74   $152.75   $152.70  
  Purchase #7 $71.66   7.539%   $77.0624   $77.06   $77.05   $77.10  
  7 purchase totals = $987.18       $1,066.8722   $1,066.88   $1,066.90   $1,066.70