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 $91.35   11.580%   $101.9283   $101.93   $101.95   $101.90  
  Purchase #2 $166.53   11.654%   $185.9374   $185.94   $185.95   $185.90  
  Purchase #3 $181.45   7.426%   $194.9245   $194.92   $194.90   $194.90  
  Purchase #4 $156.30   7.286%   $167.688   $167.69   $167.70   $167.70  
  Purchase #5 $146.76   3.144%   $151.3741   $151.37   $151.35   $151.40  
  Purchase #6 $203.84   4.707%   $213.4347   $213.43   $213.45   $213.40  
  Purchase #7 $148.50   8.862%   $161.6601   $161.66   $161.65   $161.70  
  7 purchase totals = $1,094.73       $1,176.9471   $1,176.94   $1,176.95   $1,176.90