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 $176.33   13.370%   $199.9053   $199.91   $199.90   $199.90  
  Purchase #2 $157.53   3.737%   $163.4169   $163.42   $163.40   $163.40  
  Purchase #3 $226.38   12.235%   $254.0776   $254.08   $254.10   $254.10  
  Purchase #4 $110.36   13.700%   $125.4793   $125.48   $125.50   $125.50  
  Purchase #5 $23.39   5.137%   $24.5915   $24.59   $24.60   $24.60  
  Purchase #6 $87.53   12.114%   $98.1334   $98.13   $98.15   $98.10  
  Purchase #7 $170.66   13.570%   $193.8186   $193.82   $193.80   $193.80  
  7 purchase totals = $952.18       $1,059.4226   $1,059.43   $1,059.45   $1,059.40