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 $246.34   12.290%   $276.6152   $276.62   $276.60   $276.60  
  Purchase #2 $81.35   3.235%   $83.9817   $83.98   $84.00   $84.00  
  Purchase #3 $78.83   12.869%   $88.9746   $88.97   $88.95   $89.00  
  Purchase #4 $108.52   4.619%   $113.5325   $113.53   $113.55   $113.50  
  Purchase #5 $41.65   10.663%   $46.0911   $46.09   $46.10   $46.10  
  Purchase #6 $223.62   5.458%   $235.8252   $235.83   $235.85   $235.80  
  Purchase #7 $157.81   4.712%   $165.246   $165.25   $165.25   $165.20  
  7 purchase totals = $938.12       $1,010.2663   $1,010.27   $1,010.30   $1,010.20