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 $85.74   9.462%   $93.8527   $93.85   $93.85   $93.90  
  Purchase #2 $198.60   12.764%   $223.9493   $223.95   $223.95   $223.90  
  Purchase #3 $240.35   11.184%   $267.2307   $267.23   $267.25   $267.20  
  Purchase #4 $247.70   6.317%   $263.3472   $263.35   $263.35   $263.30  
  Purchase #5 $20.98   4.549%   $21.9344   $21.93   $21.95   $21.90  
  Purchase #6 $131.86   11.472%   $146.987   $146.99   $147.00   $147.00  
  Purchase #7 $211.82   10.482%   $234.023   $234.02   $234.00   $234.00  
  7 purchase totals = $1,137.05       $1,251.3243   $1,251.32   $1,251.35   $1,251.20