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 $36.64   13.563%   $41.6095   $41.61   $41.60   $41.60  
  Purchase #2 $194.37   4.208%   $202.5491   $202.55   $202.55   $202.50  
  Purchase #3 $45.55   13.286%   $51.6018   $51.60   $51.60   $51.60  
  Purchase #4 $249.52   6.102%   $264.7457   $264.75   $264.75   $264.70  
  Purchase #5 $68.89   9.438%   $75.3918   $75.39   $75.40   $75.40  
  Purchase #6 $154.51   6.861%   $165.1109   $165.11   $165.10   $165.10  
  Purchase #7 $32.72   13.617%   $37.1755   $37.18   $37.20   $37.20  
  7 purchase totals = $782.20       $838.1843   $838.19   $838.20   $838.10