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 $184.68   3.680%   $191.4762   $191.48   $191.50   $191.50  
  Purchase #2 $220.96   7.590%   $237.7309   $237.73   $237.75   $237.70  
  Purchase #3 $180.64   12.234%   $202.7395   $202.74   $202.75   $202.70  
  Purchase #4 $28.26   13.793%   $32.1579   $32.16   $32.15   $32.20  
  Purchase #5 $24.34   10.229%   $26.8297   $26.83   $26.85   $26.80  
  Purchase #6 $178.92   7.398%   $192.1565   $192.16   $192.15   $192.20  
  Purchase #7 $131.87   8.425%   $142.98   $142.98   $143.00   $143.00  
  7 purchase totals = $949.67       $1,026.0707   $1,026.08   $1,026.15   $1,026.10