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 $108.61   8.264%   $117.5855   $117.59   $117.60   $117.60  
  Purchase #2 $159.38   3.765%   $165.3807   $165.38   $165.40   $165.40  
  Purchase #3 $24.60   4.606%   $25.7331   $25.73   $25.75   $25.70  
  Purchase #4 $47.51   11.308%   $52.8824   $52.88   $52.90   $52.90  
  Purchase #5 $200.64   9.437%   $219.5744   $219.57   $219.55   $219.60  
  Purchase #6 $224.83   9.736%   $246.7194   $246.72   $246.70   $246.70  
  Purchase #7 $197.35   3.770%   $204.7901   $204.79   $204.80   $204.80  
  7 purchase totals = $962.92       $1,032.6656   $1,032.66   $1,032.70   $1,032.70