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 $162.25   13.104%   $183.5112   $183.51   $183.50   $183.50  
  Purchase #2 $79.55   10.121%   $87.6013   $87.60   $87.60   $87.60  
  Purchase #3 $34.75   4.241%   $36.2237   $36.22   $36.20   $36.20  
  Purchase #4 $223.27   3.508%   $231.1023   $231.10   $231.10   $231.10  
  Purchase #5 $12.77   12.829%   $14.4083   $14.41   $14.40   $14.40  
  Purchase #6 $246.67   11.547%   $275.153   $275.15   $275.15   $275.20  
  Purchase #7 $165.78   4.793%   $173.7258   $173.73   $173.75   $173.70  
  7 purchase totals = $925.04       $1,001.7256   $1,001.72   $1,001.70   $1,001.70