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 $168.48   5.527%   $177.7919   $177.79   $177.80   $177.80  
  Purchase #2 $15.28   13.276%   $17.3086   $17.31   $17.30   $17.30  
  Purchase #3 $41.58   5.332%   $43.797   $43.80   $43.80   $43.80  
  Purchase #4 $208.60   5.130%   $219.3012   $219.30   $219.30   $219.30  
  Purchase #5 $68.98   12.844%   $77.8398   $77.84   $77.85   $77.80  
  Purchase #6 $44.47   10.414%   $49.1011   $49.10   $49.10   $49.10  
  Purchase #7 $122.51   5.152%   $128.8217   $128.82   $128.80   $128.80  
  7 purchase totals = $669.90       $713.9613   $713.96   $713.95   $713.90