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 $156.59   11.667%   $174.8594   $174.86   $174.85   $174.90  
  Purchase #2 $236.38   13.407%   $268.0715   $268.07   $268.05   $268.10  
  Purchase #3 $10.93   6.270%   $11.6153   $11.62   $11.60   $11.60  
  Purchase #4 $179.55   4.550%   $187.7195   $187.72   $187.70   $187.70  
  Purchase #5 $168.90   13.310%   $191.3806   $191.38   $191.40   $191.40  
  Purchase #6 $228.44   11.513%   $254.7403   $254.74   $254.75   $254.70  
  Purchase #7 $171.45   7.634%   $184.5385   $184.54   $184.55   $184.50  
  7 purchase totals = $1,152.24       $1,272.9251   $1,272.93   $1,272.90   $1,272.90