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 $125.82   8.272%   $136.2278   $136.23   $136.25   $136.20  
  Purchase #2 $245.85   6.834%   $262.6514   $262.65   $262.65   $262.70  
  Purchase #3 $187.91   3.792%   $195.0355   $195.04   $195.05   $195.00  
  Purchase #4 $82.69   4.573%   $86.4714   $86.47   $86.45   $86.50  
  Purchase #5 $171.51   7.494%   $184.363   $184.36   $184.35   $184.40  
  Purchase #6 $218.89   4.317%   $228.3395   $228.34   $228.35   $228.30  
  Purchase #7 $27.43   8.474%   $29.7544   $29.75   $29.75   $29.80  
  7 purchase totals = $1,060.10       $1,122.8430   $1,122.84   $1,122.85   $1,122.90