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 $174.68   10.858%   $193.6468   $193.65   $193.65   $193.60  
  Purchase #2 $59.72   9.423%   $65.3474   $65.35   $65.35   $65.30  
  Purchase #3 $158.31   3.227%   $163.4187   $163.42   $163.40   $163.40  
  Purchase #4 $205.93   12.590%   $231.8566   $231.86   $231.85   $231.90  
  Purchase #5 $156.42   3.217%   $161.452   $161.45   $161.45   $161.50  
  Purchase #6 $127.49   13.822%   $145.1117   $145.11   $145.10   $145.10  
  Purchase #7 $32.56   7.731%   $35.0772   $35.08   $35.10   $35.10  
  7 purchase totals = $915.11       $995.9104   $995.92   $995.90   $995.90