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 $25.84   5.772%   $27.3315   $27.33   $27.35   $27.30  
  Purchase #2 $244.69   5.316%   $257.6977   $257.70   $257.70   $257.70  
  Purchase #3 $212.53   13.489%   $241.1982   $241.20   $241.20   $241.20  
  Purchase #4 $102.86   8.161%   $111.2544   $111.25   $111.25   $111.30  
  Purchase #5 $11.32   8.409%   $12.2719   $12.27   $12.25   $12.30  
  Purchase #6 $41.31   5.552%   $43.6035   $43.60   $43.60   $43.60  
  Purchase #7 $36.98   7.228%   $39.6529   $39.65   $39.65   $39.70  
  7 purchase totals = $675.53       $733.0101   $733.00   $733.00   $733.10