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 $212.61   6.178%   $225.745   $225.75   $225.75   $225.70  
  Purchase #2 $12.41   5.199%   $13.0552   $13.06   $13.05   $13.10  
  Purchase #3 $173.49   9.524%   $190.0132   $190.01   $190.00   $190.00  
  Purchase #4 $83.31   4.501%   $87.0598   $87.06   $87.05   $87.10  
  Purchase #5 $243.68   11.212%   $271.0014   $271.00   $271.00   $271.00  
  Purchase #6 $156.49   6.125%   $166.075   $166.08   $166.10   $166.10  
  Purchase #7 $208.34   3.487%   $215.6048   $215.60   $215.60   $215.60  
  7 purchase totals = $1,090.33       $1,168.5544   $1,168.56   $1,168.55   $1,168.60