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 $59.85   11.250%   $66.5831   $66.58   $66.60   $66.60  
  Purchase #2 $194.69   9.647%   $213.4717   $213.47   $213.45   $213.50  
  Purchase #3 $128.27   11.411%   $142.9069   $142.91   $142.90   $142.90  
  Purchase #4 $199.86   4.582%   $209.0176   $209.02   $209.00   $209.00  
  Purchase #5 $174.70   5.521%   $184.3452   $184.35   $184.35   $184.30  
  Purchase #6 $134.72   13.681%   $153.151   $153.15   $153.15   $153.20  
  Purchase #7 $224.53   3.344%   $232.0383   $232.04   $232.05   $232.00  
  7 purchase totals = $1,116.62       $1,201.5138   $1,201.52   $1,201.50   $1,201.50