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 $56.59   9.164%   $61.7759   $61.78   $61.80   $61.80  
  Purchase #2 $158.74   7.270%   $170.2804   $170.28   $170.30   $170.30  
  Purchase #3 $128.44   3.396%   $132.8018   $132.80   $132.80   $132.80  
  Purchase #4 $153.92   3.644%   $159.5288   $159.53   $159.55   $159.50  
  Purchase #5 $11.60   11.187%   $12.8977   $12.90   $12.90   $12.90  
  Purchase #6 $88.66   4.319%   $92.4892   $92.49   $92.50   $92.50  
  Purchase #7 $114.75   7.134%   $122.9363   $122.94   $122.95   $122.90  
  7 purchase totals = $712.70       $752.7101   $752.72   $752.80   $752.70