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 $87.71   12.361%   $98.5518   $98.55   $98.55   $98.60  
  Purchase #2 $29.82   11.586%   $33.2749   $33.27   $33.25   $33.30  
  Purchase #3 $169.96   11.396%   $189.3286   $189.33   $189.35   $189.30  
  Purchase #4 $197.74   10.864%   $219.2225   $219.22   $219.20   $219.20  
  Purchase #5 $75.36   9.595%   $82.5908   $82.59   $82.60   $82.60  
  Purchase #6 $16.38   9.631%   $17.9576   $17.96   $17.95   $18.00  
  Purchase #7 $199.41   5.230%   $209.8391   $209.84   $209.85   $209.80  
  7 purchase totals = $776.38       $850.7653   $850.76   $850.75   $850.80