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 $210.96   4.157%   $219.7296   $219.73   $219.75   $219.70  
  Purchase #2 $51.76   3.753%   $53.7026   $53.70   $53.70   $53.70  
  Purchase #3 $47.72   11.229%   $53.0785   $53.08   $53.10   $53.10  
  Purchase #4 $87.74   5.683%   $92.7263   $92.73   $92.75   $92.70  
  Purchase #5 $214.76   5.185%   $225.8953   $225.90   $225.90   $225.90  
  Purchase #6 $52.96   5.717%   $55.9877   $55.99   $56.00   $56.00  
  Purchase #7 $61.75   10.596%   $68.293   $68.29   $68.30   $68.30  
  7 purchase totals = $727.65       $769.4130   $769.42   $769.50   $769.40