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 $233.74   12.501%   $262.9598   $262.96   $262.95   $263.00  
  Purchase #2 $134.30   13.631%   $152.6064   $152.61   $152.60   $152.60  
  Purchase #3 $80.81   13.435%   $91.6668   $91.67   $91.65   $91.70  
  Purchase #4 $93.89   8.651%   $102.0124   $102.01   $102.00   $102.00  
  Purchase #5 $45.29   5.559%   $47.8077   $47.81   $47.80   $47.80  
  Purchase #6 $34.65   13.790%   $39.4282   $39.43   $39.45   $39.40  
  Purchase #7 $183.47   6.719%   $195.7973   $195.80   $195.80   $195.80  
  7 purchase totals = $806.15       $892.2786   $892.29   $892.25   $892.30