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 $202.93   11.789%   $226.8534   $226.85   $226.85   $226.90  
  Purchase #2 $200.95   4.854%   $210.7041   $210.70   $210.70   $210.70  
  Purchase #3 $202.53   5.847%   $214.3719   $214.37   $214.35   $214.40  
  Purchase #4 $187.52   8.702%   $203.838   $203.84   $203.85   $203.80  
  Purchase #5 $48.63   6.867%   $51.9694   $51.97   $51.95   $52.00  
  Purchase #6 $85.90   9.248%   $93.844   $93.84   $93.85   $93.80  
  Purchase #7 $179.52   5.286%   $189.0094   $189.01   $189.00   $189.00  
  7 purchase totals = $1,107.98       $1,190.5902   $1,190.58   $1,190.55   $1,190.60