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 $240.73   10.691%   $266.4664   $266.47   $266.45   $266.50  
  Purchase #2 $132.52   3.132%   $136.6705   $136.67   $136.65   $136.70  
  Purchase #3 $151.70   13.290%   $171.8609   $171.86   $171.85   $171.90  
  Purchase #4 $89.73   3.123%   $92.5323   $92.53   $92.55   $92.50  
  Purchase #5 $204.36   8.120%   $220.954   $220.95   $220.95   $221.00  
  Purchase #6 $80.44   9.398%   $87.9998   $88.00   $88.00   $88.00  
  Purchase #7 $179.25   6.595%   $191.0715   $191.07   $191.05   $191.10  
  7 purchase totals = $1,078.73       $1,167.5554   $1,167.55   $1,167.50   $1,167.70