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 $42.66   7.563%   $45.8864   $45.89   $45.90   $45.90  
  Purchase #2 $244.82   11.798%   $273.7039   $273.70   $273.70   $273.70  
  Purchase #3 $156.25   12.173%   $175.2703   $175.27   $175.25   $175.30  
  Purchase #4 $186.61   13.450%   $211.709   $211.71   $211.70   $211.70  
  Purchase #5 $231.31   7.214%   $247.9967   $248.00   $248.00   $248.00  
  Purchase #6 $176.56   3.280%   $182.3512   $182.35   $182.35   $182.40  
  Purchase #7 $204.82   9.833%   $224.96   $224.96   $224.95   $225.00  
  7 purchase totals = $1,243.03       $1,361.8775   $1,361.88   $1,361.85   $1,362.00