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 $173.27   7.869%   $186.9046   $186.90   $186.90   $186.90  
  Purchase #2 $135.52   10.371%   $149.5748   $149.57   $149.55   $149.60  
  Purchase #3 $250.30   9.214%   $273.3626   $273.36   $273.35   $273.40  
  Purchase #4 $85.62   11.508%   $95.4731   $95.47   $95.45   $95.50  
  Purchase #5 $204.99   12.367%   $230.3411   $230.34   $230.35   $230.30  
  Purchase #6 $124.42   9.150%   $135.8044   $135.80   $135.80   $135.80  
  Purchase #7 $180.85   7.508%   $194.4282   $194.43   $194.45   $194.40  
  7 purchase totals = $1,154.97       $1,265.8888   $1,265.87   $1,265.85   $1,265.90