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 $169.35   6.124%   $179.721   $179.72   $179.70   $179.70  
  Purchase #2 $224.39   12.153%   $251.6601   $251.66   $251.65   $251.70  
  Purchase #3 $217.68   10.503%   $240.5429   $240.54   $240.55   $240.50  
  Purchase #4 $185.72   4.407%   $193.9047   $193.90   $193.90   $193.90  
  Purchase #5 $47.64   12.346%   $53.5216   $53.52   $53.50   $53.50  
  Purchase #6 $200.43   10.742%   $221.9602   $221.96   $221.95   $222.00  
  Purchase #7 $31.71   9.216%   $34.6324   $34.63   $34.65   $34.60  
  7 purchase totals = $1,076.92       $1,175.9429   $1,175.93   $1,175.90   $1,175.90