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 $185.26   5.249%   $194.9843   $194.98   $195.00   $195.00  
  Purchase #2 $223.39   3.328%   $230.8244   $230.82   $230.80   $230.80  
  Purchase #3 $163.47   9.166%   $178.4537   $178.45   $178.45   $178.50  
  Purchase #4 $74.28   4.143%   $77.3574   $77.36   $77.35   $77.40  
  Purchase #5 $242.41   11.199%   $269.5575   $269.56   $269.55   $269.60  
  Purchase #6 $34.32   11.230%   $38.1741   $38.17   $38.15   $38.20  
  Purchase #7 $228.47   13.618%   $259.583   $259.58   $259.60   $259.60  
  7 purchase totals = $1,151.60       $1,248.9344   $1,248.92   $1,248.90   $1,249.10