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 $81.84   8.504%   $88.7997   $88.80   $88.80   $88.80  
  Purchase #2 $220.46   3.253%   $227.6316   $227.63   $227.65   $227.60  
  Purchase #3 $45.91   12.769%   $51.7722   $51.77   $51.75   $51.80  
  Purchase #4 $166.82   7.842%   $179.902   $179.90   $179.90   $179.90  
  Purchase #5 $241.92   9.302%   $264.4234   $264.42   $264.40   $264.40  
  Purchase #6 $35.64   7.452%   $38.2959   $38.30   $38.30   $38.30  
  Purchase #7 $202.62   5.148%   $213.0509   $213.05   $213.05   $213.10  
  7 purchase totals = $995.21       $1,063.8757   $1,063.87   $1,063.85   $1,063.90