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 $246.96   10.467%   $272.8093   $272.81   $272.80   $272.80  
  Purchase #2 $62.65   11.315%   $69.7388   $69.74   $69.75   $69.70  
  Purchase #3 $180.32   8.578%   $195.7878   $195.79   $195.80   $195.80  
  Purchase #4 $35.52   9.620%   $38.937   $38.94   $38.95   $38.90  
  Purchase #5 $197.25   13.506%   $223.8906   $223.89   $223.90   $223.90  
  Purchase #6 $142.89   9.583%   $156.5831   $156.58   $156.60   $156.60  
  Purchase #7 $188.31   3.381%   $194.6768   $194.68   $194.70   $194.70  
  7 purchase totals = $1,053.90       $1,152.4234   $1,152.43   $1,152.50   $1,152.40