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 $95.86   11.851%   $107.2204   $107.22   $107.20   $107.20  
  Purchase #2 $192.27   5.457%   $202.7622   $202.76   $202.75   $202.80  
  Purchase #3 $152.27   6.127%   $161.5996   $161.60   $161.60   $161.60  
  Purchase #4 $51.93   6.410%   $55.2587   $55.26   $55.25   $55.30  
  Purchase #5 $69.35   12.164%   $77.7857   $77.79   $77.80   $77.80  
  Purchase #6 $208.57   9.505%   $228.3946   $228.39   $228.40   $228.40  
  Purchase #7 $22.94   12.562%   $25.8217   $25.82   $25.80   $25.80  
  7 purchase totals = $793.19       $858.8429   $858.84   $858.80   $858.90