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 $77.71   12.615%   $87.5131   $87.51   $87.50   $87.50  
  Purchase #2 $41.32   7.326%   $44.3471   $44.35   $44.35   $44.30  
  Purchase #3 $161.86   3.599%   $167.6853   $167.69   $167.70   $167.70  
  Purchase #4 $194.57   4.208%   $202.7575   $202.76   $202.75   $202.80  
  Purchase #5 $96.48   8.551%   $104.73   $104.73   $104.75   $104.70  
  Purchase #6 $219.49   4.544%   $229.4636   $229.46   $229.45   $229.50  
  Purchase #7 $220.25   4.238%   $229.5842   $229.58   $229.60   $229.60  
  7 purchase totals = $1,011.68       $1,066.0808   $1,066.08   $1,066.10   $1,066.10