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 $228.87   8.490%   $248.3011   $248.30   $248.30   $248.30  
  Purchase #2 $32.29   4.838%   $33.8522   $33.85   $33.85   $33.90  
  Purchase #3 $181.53   5.565%   $191.6321   $191.63   $191.65   $191.60  
  Purchase #4 $180.36   8.138%   $195.0377   $195.04   $195.05   $195.00  
  Purchase #5 $218.94   4.491%   $228.7726   $228.77   $228.75   $228.80  
  Purchase #6 $236.54   4.761%   $247.8017   $247.80   $247.80   $247.80  
  Purchase #7 $49.60   5.578%   $52.3667   $52.37   $52.35   $52.40  
  7 purchase totals = $1,128.13       $1,197.7641   $1,197.76   $1,197.75   $1,197.80