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 $73.47   6.113%   $77.9612   $77.96   $77.95   $78.00  
  Purchase #2 $210.75   10.171%   $232.1854   $232.19   $232.20   $232.20  
  Purchase #3 $232.73   11.163%   $258.7096   $258.71   $258.70   $258.70  
  Purchase #4 $183.57   8.253%   $198.72   $198.72   $198.70   $198.70  
  Purchase #5 $163.70   5.573%   $172.823   $172.82   $172.80   $172.80  
  Purchase #6 $248.96   4.625%   $260.4744   $260.47   $260.45   $260.50  
  Purchase #7 $68.73   6.651%   $73.3012   $73.30   $73.30   $73.30  
  7 purchase totals = $1,181.91       $1,274.1748   $1,274.17   $1,274.10   $1,274.20