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 $59.78   11.567%   $66.6948   $66.69   $66.70   $66.70  
  Purchase #2 $189.27   9.874%   $207.9585   $207.96   $207.95   $208.00  
  Purchase #3 $100.88   8.842%   $109.7998   $109.80   $109.80   $109.80  
  Purchase #4 $156.73   8.223%   $169.6179   $169.62   $169.60   $169.60  
  Purchase #5 $28.36   11.411%   $31.5962   $31.60   $31.60   $31.60  
  Purchase #6 $235.45   12.266%   $264.3303   $264.33   $264.35   $264.30  
  Purchase #7 $56.65   6.438%   $60.2971   $60.30   $60.30   $60.30  
  7 purchase totals = $827.12       $910.2946   $910.30   $910.30   $910.30