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 $93.75   10.707%   $103.7878   $103.79   $103.80   $103.80  
  Purchase #2 $29.46   9.358%   $32.2169   $32.22   $32.20   $32.20  
  Purchase #3 $182.59   11.167%   $202.9798   $202.98   $203.00   $203.00  
  Purchase #4 $233.86   13.747%   $266.0087   $266.01   $266.00   $266.00  
  Purchase #5 $77.36   8.155%   $83.6687   $83.67   $83.65   $83.70  
  Purchase #6 $33.58   10.739%   $37.1862   $37.19   $37.20   $37.20  
  Purchase #7 $43.89   13.754%   $49.9266   $49.93   $49.95   $49.90  
  7 purchase totals = $694.49       $775.7747   $775.79   $775.80   $775.80