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 $53.98   6.199%   $57.3262   $57.33   $57.35   $57.30  
  Purchase #2 $220.29   13.444%   $249.9058   $249.91   $249.90   $249.90  
  Purchase #3 $148.98   3.431%   $154.0915   $154.09   $154.10   $154.10  
  Purchase #4 $76.62   4.867%   $80.3491   $80.35   $80.35   $80.30  
  Purchase #5 $171.85   11.318%   $191.3   $191.30   $191.30   $191.30  
  Purchase #6 $177.32   8.818%   $192.9561   $192.96   $192.95   $193.00  
  Purchase #7 $193.29   3.868%   $200.7665   $200.77   $200.75   $200.80  
  7 purchase totals = $1,042.33       $1,126.6952   $1,126.71   $1,126.70   $1,126.70