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 $134.92   8.705%   $146.6648   $146.66   $146.65   $146.70  
  Purchase #2 $110.73   6.846%   $118.3106   $118.31   $118.30   $118.30  
  Purchase #3 $84.78   3.801%   $88.0025   $88.00   $88.00   $88.00  
  Purchase #4 $13.78   5.409%   $14.5254   $14.53   $14.55   $14.50  
  Purchase #5 $55.54   5.342%   $58.5069   $58.51   $58.50   $58.50  
  Purchase #6 $194.45   12.575%   $218.9021   $218.90   $218.90   $218.90  
  Purchase #7 $235.60   5.594%   $248.7795   $248.78   $248.80   $248.80  
  7 purchase totals = $829.80       $893.6918   $893.69   $893.70   $893.70