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 $174.93   13.171%   $197.97   $197.97   $197.95   $198.00  
  Purchase #2 $12.29   3.804%   $12.7575   $12.76   $12.75   $12.80  
  Purchase #3 $69.49   4.519%   $72.6303   $72.63   $72.65   $72.60  
  Purchase #4 $211.27   4.325%   $220.4074   $220.41   $220.40   $220.40  
  Purchase #5 $150.92   9.468%   $165.2091   $165.21   $165.20   $165.20  
  Purchase #6 $41.91   3.226%   $43.262   $43.26   $43.25   $43.30  
  Purchase #7 $216.41   6.241%   $229.9161   $229.92   $229.90   $229.90  
  7 purchase totals = $877.22       $942.1524   $942.16   $942.10   $942.20