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 $209.29   7.749%   $225.5079   $225.51   $225.50   $225.50  
  Purchase #2 $95.69   12.399%   $107.5546   $107.55   $107.55   $107.60  
  Purchase #3 $241.63   6.832%   $258.1382   $258.14   $258.15   $258.10  
  Purchase #4 $151.46   7.116%   $162.2379   $162.24   $162.25   $162.20  
  Purchase #5 $220.49   11.565%   $245.9897   $245.99   $246.00   $246.00  
  Purchase #6 $77.96   12.543%   $87.7385   $87.74   $87.75   $87.70  
  Purchase #7 $6.94   3.356%   $7.1729   $7.17   $7.15   $7.20  
  7 purchase totals = $1,003.46       $1,094.3397   $1,094.34   $1,094.35   $1,094.30