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 $55.85   5.727%   $59.0485   $59.05   $59.05   $59.00  
  Purchase #2 $230.88   3.304%   $238.5083   $238.51   $238.50   $238.50  
  Purchase #3 $92.43   12.819%   $104.2786   $104.28   $104.30   $104.30  
  Purchase #4 $56.92   3.588%   $58.9623   $58.96   $58.95   $59.00  
  Purchase #5 $104.50   9.858%   $114.8016   $114.80   $114.80   $114.80  
  Purchase #6 $191.84   8.175%   $207.5229   $207.52   $207.50   $207.50  
  Purchase #7 $220.89   11.433%   $246.1444   $246.14   $246.15   $246.10  
  7 purchase totals = $953.31       $1,029.2666   $1,029.26   $1,029.25   $1,029.20