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 $79.90   9.443%   $87.445   $87.45   $87.45   $87.40  
  Purchase #2 $171.26   4.413%   $178.8177   $178.82   $178.80   $178.80  
  Purchase #3 $220.40   3.653%   $228.4512   $228.45   $228.45   $228.50  
  Purchase #4 $109.65   3.704%   $113.7114   $113.71   $113.70   $113.70  
  Purchase #5 $112.59   3.486%   $116.5149   $116.51   $116.50   $116.50  
  Purchase #6 $102.30   5.267%   $107.6881   $107.69   $107.70   $107.70  
  Purchase #7 $125.60   3.165%   $129.5752   $129.58   $129.60   $129.60  
  7 purchase totals = $921.70       $962.2035   $962.21   $962.20   $962.20