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 $232.98   8.220%   $252.131   $252.13   $252.15   $252.10  
  Purchase #2 $34.71   13.647%   $39.4469   $39.45   $39.45   $39.40  
  Purchase #3 $79.61   5.589%   $84.0594   $84.06   $84.05   $84.10  
  Purchase #4 $155.78   10.130%   $171.5605   $171.56   $171.55   $171.60  
  Purchase #5 $180.86   8.151%   $195.6019   $195.60   $195.60   $195.60  
  Purchase #6 $223.66   9.227%   $244.2971   $244.30   $244.30   $244.30  
  Purchase #7 $7.27   11.195%   $8.0839   $8.08   $8.10   $8.10  
  7 purchase totals = $914.87       $995.1807   $995.18   $995.20   $995.20