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 $44.91   8.169%   $48.5787   $48.58   $48.60   $48.60  
  Purchase #2 $228.88   7.159%   $245.2655   $245.27   $245.25   $245.30  
  Purchase #3 $89.80   4.756%   $94.0709   $94.07   $94.05   $94.10  
  Purchase #4 $219.60   12.745%   $247.588   $247.59   $247.60   $247.60  
  Purchase #5 $171.77   11.239%   $191.0752   $191.08   $191.10   $191.10  
  Purchase #6 $199.71   10.346%   $220.372   $220.37   $220.35   $220.40  
  Purchase #7 $125.91   7.445%   $135.284   $135.28   $135.30   $135.30  
  7 purchase totals = $1,080.58       $1,182.2343   $1,182.24   $1,182.25   $1,182.40