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 $167.34   7.232%   $179.442   $179.44   $179.45   $179.40  
  Purchase #2 $87.57   11.121%   $97.3087   $97.31   $97.30   $97.30  
  Purchase #3 $40.93   9.131%   $44.6673   $44.67   $44.65   $44.70  
  Purchase #4 $206.95   7.605%   $222.6885   $222.69   $222.70   $222.70  
  Purchase #5 $8.30   13.652%   $9.4331   $9.43   $9.45   $9.40  
  Purchase #6 $194.49   9.701%   $213.3575   $213.36   $213.35   $213.40  
  Purchase #7 $238.31   7.703%   $256.667   $256.67   $256.65   $256.70  
  7 purchase totals = $943.89       $1,023.5641   $1,023.57   $1,023.55   $1,023.60