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 $246.67   7.263%   $264.5856   $264.59   $264.60   $264.60  
  Purchase #2 $99.79   8.828%   $108.5995   $108.60   $108.60   $108.60  
  Purchase #3 $110.32   11.163%   $122.635   $122.64   $122.65   $122.60  
  Purchase #4 $248.28   8.504%   $269.3937   $269.39   $269.40   $269.40  
  Purchase #5 $183.41   4.477%   $191.6213   $191.62   $191.60   $191.60  
  Purchase #6 $201.74   4.755%   $211.3327   $211.33   $211.35   $211.30  
  Purchase #7 $60.92   3.322%   $62.9438   $62.94   $62.95   $62.90  
  7 purchase totals = $1,151.13       $1,231.1116   $1,231.11   $1,231.15   $1,231.00