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 $232.31   6.658%   $247.7772   $247.78   $247.80   $247.80  
  Purchase #2 $77.73   8.347%   $84.2181   $84.22   $84.20   $84.20  
  Purchase #3 $43.77   4.123%   $45.5746   $45.57   $45.55   $45.60  
  Purchase #4 $107.74   9.663%   $118.1509   $118.15   $118.15   $118.20  
  Purchase #5 $222.51   11.839%   $248.853   $248.85   $248.85   $248.90  
  Purchase #6 $120.64   13.407%   $136.8142   $136.81   $136.80   $136.80  
  Purchase #7 $148.59   9.668%   $162.9557   $162.96   $162.95   $163.00  
  7 purchase totals = $953.29       $1,044.3437   $1,044.34   $1,044.30   $1,044.50