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 $156.38   6.120%   $165.9505   $165.95   $165.95   $166.00  
  Purchase #2 $60.71   6.234%   $64.4947   $64.49   $64.50   $64.50  
  Purchase #3 $227.27   7.367%   $244.013   $244.01   $244.00   $244.00  
  Purchase #4 $221.85   4.640%   $232.1438   $232.14   $232.15   $232.10  
  Purchase #5 $228.98   5.200%   $240.887   $240.89   $240.90   $240.90  
  Purchase #6 $152.31   7.245%   $163.3449   $163.34   $163.35   $163.30  
  Purchase #7 $156.37   4.846%   $163.9477   $163.95   $163.95   $163.90  
  7 purchase totals = $1,203.87       $1,274.7816   $1,274.77   $1,274.80   $1,274.70