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 $69.72   11.406%   $77.6723   $77.67   $77.65   $77.70  
  Purchase #2 $224.91   4.791%   $235.6854   $235.69   $235.70   $235.70  
  Purchase #3 $162.83   4.392%   $169.9815   $169.98   $170.00   $170.00  
  Purchase #4 $65.72   6.781%   $70.1765   $70.18   $70.20   $70.20  
  Purchase #5 $153.45   11.112%   $170.5014   $170.50   $170.50   $170.50  
  Purchase #6 $172.72   10.810%   $191.391   $191.39   $191.40   $191.40  
  Purchase #7 $62.89   12.190%   $70.5563   $70.56   $70.55   $70.60  
  7 purchase totals = $912.24       $985.9644   $985.97   $986.00   $986.10