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 $91.77   4.725%   $96.1061   $96.11   $96.10   $96.10  
  Purchase #2 $226.86   12.695%   $255.6599   $255.66   $255.65   $255.70  
  Purchase #3 $211.88   8.719%   $230.3538   $230.35   $230.35   $230.40  
  Purchase #4 $99.27   9.764%   $108.9627   $108.96   $108.95   $109.00  
  Purchase #5 $177.52   7.442%   $190.731   $190.73   $190.75   $190.70  
  Purchase #6 $105.26   11.363%   $117.2207   $117.22   $117.20   $117.20  
  Purchase #7 $36.49   13.711%   $41.4931   $41.49   $41.50   $41.50  
  7 purchase totals = $949.05       $1,040.5273   $1,040.52   $1,040.50   $1,040.60