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 $82.92   13.815%   $94.3754   $94.38   $94.40   $94.40  
  Purchase #2 $112.79   6.397%   $120.0052   $120.01   $120.00   $120.00  
  Purchase #3 $24.86   5.730%   $26.2845   $26.28   $26.30   $26.30  
  Purchase #4 $232.27   10.627%   $256.9533   $256.95   $256.95   $257.00  
  Purchase #5 $98.86   12.842%   $111.5556   $111.56   $111.55   $111.60  
  Purchase #6 $201.82   8.514%   $219.003   $219.00   $219.00   $219.00  
  Purchase #7 $241.59   5.417%   $254.6769   $254.68   $254.70   $254.70  
  7 purchase totals = $995.11       $1,082.8539   $1,082.86   $1,082.90   $1,083.00