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 $52.73   7.521%   $56.6958   $56.70   $56.70   $56.70  
  Purchase #2 $146.92   9.337%   $160.6379   $160.64   $160.65   $160.60  
  Purchase #3 $126.92   12.381%   $142.634   $142.63   $142.65   $142.60  
  Purchase #4 $83.34   5.599%   $88.0062   $88.01   $88.00   $88.00  
  Purchase #5 $155.48   12.230%   $174.4952   $174.50   $174.50   $174.50  
  Purchase #6 $246.60   10.460%   $272.3944   $272.39   $272.40   $272.40  
  Purchase #7 $176.80   13.215%   $200.1641   $200.16   $200.15   $200.20  
  7 purchase totals = $988.79       $1,095.0276   $1,095.03   $1,095.05   $1,095.00