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 $155.75   11.757%   $174.0615   $174.06   $174.05   $174.10  
  Purchase #2 $75.47   8.328%   $81.7551   $81.76   $81.75   $81.80  
  Purchase #3 $163.93   5.478%   $172.9101   $172.91   $172.90   $172.90  
  Purchase #4 $56.59   11.297%   $62.983   $62.98   $63.00   $63.00  
  Purchase #5 $134.46   8.305%   $145.6269   $145.63   $145.65   $145.60  
  Purchase #6 $158.56   5.476%   $167.2427   $167.24   $167.25   $167.20  
  Purchase #7 $211.66   12.259%   $237.6074   $237.61   $237.60   $237.60  
  7 purchase totals = $956.42       $1,042.1867   $1,042.19   $1,042.20   $1,042.20