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 $40.84   9.752%   $44.8227   $44.82   $44.80   $44.80  
  Purchase #2 $163.82   5.740%   $173.2233   $173.22   $173.20   $173.20  
  Purchase #3 $220.39   8.837%   $239.8659   $239.87   $239.85   $239.90  
  Purchase #4 $191.62   7.286%   $205.5814   $205.58   $205.60   $205.60  
  Purchase #5 $119.71   6.284%   $127.2326   $127.23   $127.25   $127.20  
  Purchase #6 $172.73   8.537%   $187.476   $187.48   $187.50   $187.50  
  Purchase #7 $228.57   12.494%   $257.1275   $257.13   $257.15   $257.10  
  7 purchase totals = $1,137.68       $1,235.3294   $1,235.33   $1,235.35   $1,235.30