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 $144.31   12.266%   $162.0111   $162.01   $162.00   $162.00  
  Purchase #2 $45.37   3.240%   $46.84   $46.84   $46.85   $46.80  
  Purchase #3 $83.95   8.810%   $91.346   $91.35   $91.35   $91.30  
  Purchase #4 $238.60   8.867%   $259.7567   $259.76   $259.75   $259.80  
  Purchase #5 $175.40   4.547%   $183.3754   $183.38   $183.40   $183.40  
  Purchase #6 $138.71   7.619%   $149.2783   $149.28   $149.30   $149.30  
  Purchase #7 $247.93   4.278%   $258.5364   $258.54   $258.55   $258.50  
  7 purchase totals = $1,074.27       $1,151.1439   $1,151.16   $1,151.20   $1,151.10