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 $74.88   11.266%   $83.316   $83.32   $83.30   $83.30  
  Purchase #2 $174.56   3.818%   $181.2247   $181.22   $181.20   $181.20  
  Purchase #3 $95.31   9.606%   $104.4655   $104.47   $104.45   $104.50  
  Purchase #4 $27.50   4.618%   $28.77   $28.77   $28.75   $28.80  
  Purchase #5 $139.34   9.771%   $152.9549   $152.95   $152.95   $153.00  
  Purchase #6 $220.47   12.195%   $247.3563   $247.36   $247.35   $247.40  
  Purchase #7 $209.29   7.623%   $225.2442   $225.24   $225.25   $225.20  
  7 purchase totals = $941.35       $1,023.3316   $1,023.33   $1,023.25   $1,023.40