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 $187.37   8.183%   $202.7025   $202.70   $202.70   $202.70  
  Purchase #2 $193.81   12.451%   $217.9413   $217.94   $217.95   $217.90  
  Purchase #3 $149.30   8.860%   $162.528   $162.53   $162.55   $162.50  
  Purchase #4 $96.43   6.693%   $102.8841   $102.88   $102.90   $102.90  
  Purchase #5 $73.35   9.125%   $80.0432   $80.04   $80.05   $80.00  
  Purchase #6 $227.71   13.332%   $258.0683   $258.07   $258.05   $258.10  
  Purchase #7 $43.33   7.853%   $46.7327   $46.73   $46.75   $46.70  
  7 purchase totals = $971.30       $1,070.9001   $1,070.89   $1,070.95   $1,070.80