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 $95.46   12.860%   $107.7362   $107.74   $107.75   $107.70  
  Purchase #2 $211.51   11.418%   $235.6602   $235.66   $235.65   $235.70  
  Purchase #3 $129.41   8.661%   $140.6182   $140.62   $140.60   $140.60  
  Purchase #4 $88.45   10.663%   $97.8814   $97.88   $97.90   $97.90  
  Purchase #5 $170.85   13.321%   $193.6089   $193.61   $193.60   $193.60  
  Purchase #6 $95.48   11.113%   $106.0907   $106.09   $106.10   $106.10  
  Purchase #7 $200.67   13.515%   $227.7906   $227.79   $227.80   $227.80  
  7 purchase totals = $991.83       $1,109.3862   $1,109.39   $1,109.40   $1,109.40