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 $31.67   8.812%   $34.4608   $34.46   $34.45   $34.50  
  Purchase #2 $47.72   10.384%   $52.6752   $52.68   $52.70   $52.70  
  Purchase #3 $232.65   6.207%   $247.0906   $247.09   $247.10   $247.10  
  Purchase #4 $172.84   9.560%   $189.3635   $189.36   $189.35   $189.40  
  Purchase #5 $85.83   5.542%   $90.5867   $90.59   $90.60   $90.60  
  Purchase #6 $166.45   13.139%   $188.3199   $188.32   $188.30   $188.30  
  Purchase #7 $222.70   3.378%   $230.2228   $230.22   $230.20   $230.20  
  7 purchase totals = $959.86       $1,032.7195   $1,032.72   $1,032.70   $1,032.80