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 $54.42   13.515%   $61.7749   $61.77   $61.75   $61.80  
  Purchase #2 $193.83   6.442%   $206.3165   $206.32   $206.30   $206.30  
  Purchase #3 $88.47   10.367%   $97.6417   $97.64   $97.65   $97.60  
  Purchase #4 $213.72   6.805%   $228.2636   $228.26   $228.25   $228.30  
  Purchase #5 $173.64   13.870%   $197.7239   $197.72   $197.70   $197.70  
  Purchase #6 $154.95   11.169%   $172.2564   $172.26   $172.25   $172.30  
  Purchase #7 $174.76   13.193%   $197.8161   $197.82   $197.80   $197.80  
  7 purchase totals = $1,053.79       $1,161.7931   $1,161.79   $1,161.70   $1,161.80