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 $150.84   5.841%   $159.6506   $159.65   $159.65   $159.70  
  Purchase #2 $125.55   10.157%   $138.3021   $138.30   $138.30   $138.30  
  Purchase #3 $74.92   9.416%   $81.9745   $81.97   $81.95   $82.00  
  Purchase #4 $218.46   12.833%   $246.495   $246.50   $246.50   $246.50  
  Purchase #5 $53.28   7.495%   $57.2733   $57.27   $57.25   $57.30  
  Purchase #6 $159.86   8.380%   $173.2563   $173.26   $173.25   $173.30  
  Purchase #7 $143.90   9.807%   $158.0123   $158.01   $158.00   $158.00  
  7 purchase totals = $926.81       $1,014.9641   $1,014.96   $1,014.90   $1,015.10