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 $23.82   10.677%   $26.3633   $26.36   $26.35   $26.40  
  Purchase #2 $54.68   11.115%   $60.7577   $60.76   $60.75   $60.80  
  Purchase #3 $220.99   9.835%   $242.7244   $242.72   $242.70   $242.70  
  Purchase #4 $88.74   13.409%   $100.6391   $100.64   $100.65   $100.60  
  Purchase #5 $188.72   7.312%   $202.5192   $202.52   $202.50   $202.50  
  Purchase #6 $76.94   8.795%   $83.7069   $83.71   $83.70   $83.70  
  Purchase #7 $218.77   10.144%   $240.962   $240.96   $240.95   $241.00  
  7 purchase totals = $872.66       $957.6726   $957.67   $957.60   $957.70