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 $54.79   12.842%   $61.8261   $61.83   $61.85   $61.80  
  Purchase #2 $219.40   9.809%   $240.9209   $240.92   $240.90   $240.90  
  Purchase #3 $165.95   7.376%   $178.1905   $178.19   $178.20   $178.20  
  Purchase #4 $35.71   4.611%   $37.3566   $37.36   $37.35   $37.40  
  Purchase #5 $182.68   3.816%   $189.6511   $189.65   $189.65   $189.70  
  Purchase #6 $50.98   11.143%   $56.6607   $56.66   $56.65   $56.70  
  Purchase #7 $165.49   10.658%   $183.1279   $183.13   $183.15   $183.10  
  7 purchase totals = $875.00       $947.7338   $947.74   $947.75   $947.80