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 $209.27   6.764%   $223.425   $223.43   $223.45   $223.40  
  Purchase #2 $194.72   11.734%   $217.5684   $217.57   $217.55   $217.60  
  Purchase #3 $147.94   4.851%   $155.1166   $155.12   $155.10   $155.10  
  Purchase #4 $119.84   4.722%   $125.4988   $125.50   $125.50   $125.50  
  Purchase #5 $101.75   11.524%   $113.4757   $113.48   $113.50   $113.50  
  Purchase #6 $93.29   13.728%   $106.0969   $106.10   $106.10   $106.10  
  Purchase #7 $128.50   9.328%   $140.4865   $140.49   $140.50   $140.50  
  7 purchase totals = $995.31       $1,081.6679   $1,081.69   $1,081.70   $1,081.70