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 $217.99   11.504%   $243.0676   $243.07   $243.05   $243.10  
  Purchase #2 $73.40   9.638%   $80.4743   $80.47   $80.45   $80.50  
  Purchase #3 $87.34   8.411%   $94.6862   $94.69   $94.70   $94.70  
  Purchase #4 $237.43   3.476%   $245.6831   $245.68   $245.70   $245.70  
  Purchase #5 $65.70   9.701%   $72.0736   $72.07   $72.05   $72.10  
  Purchase #6 $184.97   9.440%   $202.4312   $202.43   $202.45   $202.40  
  Purchase #7 $71.54   5.582%   $75.5334   $75.53   $75.55   $75.50  
  7 purchase totals = $938.37       $1,013.9494   $1,013.94   $1,013.95   $1,014.00