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 $93.60   13.613%   $106.3418   $106.34   $106.35   $106.30  
  Purchase #2 $165.55   9.474%   $181.2342   $181.23   $181.25   $181.20  
  Purchase #3 $94.36   6.544%   $100.5349   $100.53   $100.55   $100.50  
  Purchase #4 $153.88   10.321%   $169.762   $169.76   $169.75   $169.80  
  Purchase #5 $60.68   8.818%   $66.0308   $66.03   $66.05   $66.00  
  Purchase #6 $230.27   5.739%   $243.4852   $243.49   $243.50   $243.50  
  Purchase #7 $161.51   11.515%   $180.1079   $180.11   $180.10   $180.10  
  7 purchase totals = $959.85       $1,047.4968   $1,047.49   $1,047.55   $1,047.40