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 $82.71   11.412%   $92.1489   $92.15   $92.15   $92.10  
  Purchase #2 $178.54   8.502%   $193.7195   $193.72   $193.70   $193.70  
  Purchase #3 $233.80   5.147%   $245.8337   $245.83   $245.85   $245.80  
  Purchase #4 $39.77   8.311%   $43.0753   $43.08   $43.10   $43.10  
  Purchase #5 $51.78   12.848%   $58.4327   $58.43   $58.45   $58.40  
  Purchase #6 $196.61   3.738%   $203.9593   $203.96   $203.95   $204.00  
  Purchase #7 $175.36   6.674%   $187.0635   $187.06   $187.05   $187.10  
  7 purchase totals = $958.57       $1,024.2329   $1,024.23   $1,024.25   $1,024.20