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 $153.47   8.821%   $167.0076   $167.01   $167.00   $167.00  
  Purchase #2 $62.67   5.354%   $66.0254   $66.03   $66.05   $66.00  
  Purchase #3 $185.42   8.104%   $200.4464   $200.45   $200.45   $200.40  
  Purchase #4 $124.71   5.672%   $131.7836   $131.78   $131.80   $131.80  
  Purchase #5 $224.51   10.363%   $247.776   $247.78   $247.80   $247.80  
  Purchase #6 $52.97   7.150%   $56.7574   $56.76   $56.75   $56.80  
  Purchase #7 $167.79   11.427%   $186.9634   $186.96   $186.95   $187.00  
  7 purchase totals = $971.54       $1,056.7598   $1,056.77   $1,056.80   $1,056.80