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 $31.38   13.238%   $35.5341   $35.53   $35.55   $35.50  
  Purchase #2 $249.99   9.603%   $273.9965   $274.00   $274.00   $274.00  
  Purchase #3 $94.36   9.667%   $103.4818   $103.48   $103.50   $103.50  
  Purchase #4 $159.93   12.104%   $179.2879   $179.29   $179.30   $179.30  
  Purchase #5 $197.65   11.533%   $220.445   $220.45   $220.45   $220.40  
  Purchase #6 $126.99   12.683%   $143.0961   $143.10   $143.10   $143.10  
  Purchase #7 $88.44   4.542%   $92.4569   $92.46   $92.45   $92.50  
  7 purchase totals = $948.74       $1,048.2983   $1,048.31   $1,048.35   $1,048.30