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 $45.29   9.577%   $49.6274   $49.63   $49.65   $49.60  
  Purchase #2 $172.87   12.761%   $194.9299   $194.93   $194.95   $194.90  
  Purchase #3 $246.93   6.297%   $262.4792   $262.48   $262.50   $262.50  
  Purchase #4 $91.31   5.492%   $96.3247   $96.32   $96.30   $96.30  
  Purchase #5 $208.99   11.155%   $232.3028   $232.30   $232.30   $232.30  
  Purchase #6 $225.76   5.356%   $237.8517   $237.85   $237.85   $237.90  
  Purchase #7 $243.77   10.674%   $269.79   $269.79   $269.80   $269.80  
  7 purchase totals = $1,234.92       $1,343.3057   $1,343.30   $1,343.35   $1,343.30