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 $153.62   7.623%   $165.3305   $165.33   $165.35   $165.30  
  Purchase #2 $246.84   8.464%   $267.7325   $267.73   $267.75   $267.70  
  Purchase #3 $155.52   4.717%   $162.8559   $162.86   $162.85   $162.90  
  Purchase #4 $171.62   13.360%   $194.5484   $194.55   $194.55   $194.50  
  Purchase #5 $104.93   8.296%   $113.635   $113.64   $113.65   $113.60  
  Purchase #6 $137.51   12.406%   $154.5695   $154.57   $154.55   $154.60  
  Purchase #7 $232.98   6.347%   $247.7672   $247.77   $247.75   $247.80  
  7 purchase totals = $1,203.02       $1,306.4390   $1,306.45   $1,306.45   $1,306.40