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 $212.95   12.270%   $239.079   $239.08   $239.10   $239.10  
  Purchase #2 $76.51   4.261%   $79.7701   $79.77   $79.75   $79.80  
  Purchase #3 $144.74   6.143%   $153.6314   $153.63   $153.65   $153.60  
  Purchase #4 $161.73   6.267%   $171.8656   $171.87   $171.85   $171.90  
  Purchase #5 $189.68   5.435%   $199.9891   $199.99   $200.00   $200.00  
  Purchase #6 $165.95   12.860%   $187.2912   $187.29   $187.30   $187.30  
  Purchase #7 $204.73   8.665%   $222.4699   $222.47   $222.45   $222.50  
  7 purchase totals = $1,156.29       $1,254.0963   $1,254.10   $1,254.10   $1,254.20