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 $213.99   5.648%   $226.0762   $226.08   $226.10   $226.10  
  Purchase #2 $228.78   11.717%   $255.5862   $255.59   $255.60   $255.60  
  Purchase #3 $162.29   9.426%   $177.5875   $177.59   $177.60   $177.60  
  Purchase #4 $213.83   6.230%   $227.1516   $227.15   $227.15   $227.20  
  Purchase #5 $98.54   12.146%   $110.5087   $110.51   $110.50   $110.50  
  Purchase #6 $167.52   7.734%   $180.476   $180.48   $180.50   $180.50  
  Purchase #7 $23.78   10.404%   $26.2541   $26.25   $26.25   $26.30  
  7 purchase totals = $1,108.73       $1,203.6403   $1,203.65   $1,203.70   $1,203.80