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 $217.26   13.525%   $246.6444   $246.64   $246.65   $246.60  
  Purchase #2 $165.30   9.480%   $180.9704   $180.97   $180.95   $181.00  
  Purchase #3 $91.54   9.692%   $100.4121   $100.41   $100.40   $100.40  
  Purchase #4 $244.67   9.413%   $267.7008   $267.70   $267.70   $267.70  
  Purchase #5 $231.64   4.299%   $241.5982   $241.60   $241.60   $241.60  
  Purchase #6 $56.81   4.123%   $59.1523   $59.15   $59.15   $59.20  
  Purchase #7 $62.87   6.319%   $66.8428   $66.84   $66.85   $66.80  
  7 purchase totals = $1,070.09       $1,163.3210   $1,163.31   $1,163.30   $1,163.30