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 $237.59   10.532%   $262.613   $262.61   $262.60   $262.60  
  Purchase #2 $14.55   12.444%   $16.3606   $16.36   $16.35   $16.40  
  Purchase #3 $169.89   8.416%   $184.1879   $184.19   $184.20   $184.20  
  Purchase #4 $124.85   13.547%   $141.7634   $141.76   $141.75   $141.80  
  Purchase #5 $147.84   5.119%   $155.4079   $155.41   $155.40   $155.40  
  Purchase #6 $245.72   9.735%   $269.6408   $269.64   $269.65   $269.60  
  Purchase #7 $194.97   8.764%   $212.0572   $212.06   $212.05   $212.10  
  7 purchase totals = $1,135.41       $1,242.0308   $1,242.03   $1,242.00   $1,242.10