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 $236.78   8.677%   $257.3254   $257.33   $257.35   $257.30  
  Purchase #2 $30.54   9.147%   $33.3335   $33.33   $33.35   $33.30  
  Purchase #3 $250.70   5.144%   $263.596   $263.60   $263.60   $263.60  
  Purchase #4 $206.59   9.225%   $225.6479   $225.65   $225.65   $225.60  
  Purchase #5 $55.43   9.151%   $60.5024   $60.50   $60.50   $60.50  
  Purchase #6 $127.99   8.353%   $138.681   $138.68   $138.70   $138.70  
  Purchase #7 $165.77   4.262%   $172.8351   $172.84   $172.85   $172.80  
  7 purchase totals = $1,073.80       $1,151.9213   $1,151.93   $1,152.00   $1,151.80