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 $57.92   13.633%   $65.8162   $65.82   $65.80   $65.80  
  Purchase #2 $201.47   10.526%   $222.6767   $222.68   $222.70   $222.70  
  Purchase #3 $188.35   3.371%   $194.6993   $194.70   $194.70   $194.70  
  Purchase #4 $248.65   9.521%   $272.324   $272.32   $272.30   $272.30  
  Purchase #5 $247.54   7.698%   $266.5956   $266.60   $266.60   $266.60  
  Purchase #6 $187.81   9.326%   $205.3252   $205.33   $205.35   $205.30  
  Purchase #7 $205.50   6.111%   $218.0581   $218.06   $218.05   $218.10  
  7 purchase totals = $1,337.24       $1,445.4951   $1,445.51   $1,445.50   $1,445.50