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 $69.40   11.182%   $77.1603   $77.16   $77.15   $77.20  
  Purchase #2 $70.84   7.165%   $75.9157   $75.92   $75.90   $75.90  
  Purchase #3 $188.40   9.859%   $206.9744   $206.97   $206.95   $207.00  
  Purchase #4 $195.27   8.433%   $211.7371   $211.74   $211.75   $211.70  
  Purchase #5 $12.46   13.362%   $14.1249   $14.12   $14.10   $14.10  
  Purchase #6 $225.40   9.297%   $246.3554   $246.36   $246.35   $246.40  
  Purchase #7 $156.96   7.416%   $168.6002   $168.60   $168.60   $168.60  
  7 purchase totals = $918.73       $1,000.8680   $1,000.87   $1,000.80   $1,000.90