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 $77.62   13.819%   $88.3463   $88.35   $88.35   $88.30  
  Purchase #2 $228.48   11.323%   $254.3508   $254.35   $254.35   $254.40  
  Purchase #3 $182.45   3.504%   $188.843   $188.84   $188.85   $188.80  
  Purchase #4 $120.87   11.457%   $134.7181   $134.72   $134.70   $134.70  
  Purchase #5 $207.70   5.375%   $218.8639   $218.86   $218.85   $218.90  
  Purchase #6 $5.86   12.563%   $6.5962   $6.60   $6.60   $6.60  
  Purchase #7 $231.40   4.193%   $241.1026   $241.10   $241.10   $241.10  
  7 purchase totals = $1,054.38       $1,132.8209   $1,132.82   $1,132.80   $1,132.80