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 $136.57   9.558%   $149.6234   $149.62   $149.60   $149.60  
  Purchase #2 $193.85   9.488%   $212.2425   $212.24   $212.25   $212.20  
  Purchase #3 $154.39   11.447%   $172.063   $172.06   $172.05   $172.10  
  Purchase #4 $45.27   10.470%   $50.0098   $50.01   $50.00   $50.00  
  Purchase #5 $52.71   8.597%   $57.2415   $57.24   $57.25   $57.20  
  Purchase #6 $247.38   10.454%   $273.2411   $273.24   $273.25   $273.20  
  Purchase #7 $124.55   6.134%   $132.1899   $132.19   $132.20   $132.20  
  7 purchase totals = $954.72       $1,046.6112   $1,046.60   $1,046.60   $1,046.50