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 $218.56   9.312%   $238.9123   $238.91   $238.90   $238.90  
  Purchase #2 $174.31   11.578%   $194.4916   $194.49   $194.50   $194.50  
  Purchase #3 $74.59   12.137%   $83.643   $83.64   $83.65   $83.60  
  Purchase #4 $74.65   7.132%   $79.974   $79.97   $79.95   $80.00  
  Purchase #5 $83.44   10.471%   $92.177   $92.18   $92.20   $92.20  
  Purchase #6 $232.31   11.669%   $259.4183   $259.42   $259.40   $259.40  
  Purchase #7 $199.41   6.106%   $211.586   $211.59   $211.60   $211.60  
  7 purchase totals = $1,057.27       $1,160.2022   $1,160.20   $1,160.20   $1,160.20