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 $87.32   13.521%   $99.1265   $99.13   $99.15   $99.10  
  Purchase #2 $168.96   5.253%   $177.8355   $177.84   $177.85   $177.80  
  Purchase #3 $214.35   9.634%   $235.0005   $235.00   $235.00   $235.00  
  Purchase #4 $198.67   13.651%   $225.7904   $225.79   $225.80   $225.80  
  Purchase #5 $112.75   4.785%   $118.1451   $118.15   $118.15   $118.10  
  Purchase #6 $25.46   4.346%   $26.5665   $26.57   $26.55   $26.60  
  Purchase #7 $154.93   11.184%   $172.2574   $172.26   $172.25   $172.30  
  7 purchase totals = $962.44       $1,054.7219   $1,054.74   $1,054.75   $1,054.70