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 $51.86   3.713%   $53.7856   $53.79   $53.80   $53.80  
  Purchase #2 $211.99   12.113%   $237.6683   $237.67   $237.65   $237.70  
  Purchase #3 $123.93   3.767%   $128.5984   $128.60   $128.60   $128.60  
  Purchase #4 $113.89   6.483%   $121.2735   $121.27   $121.25   $121.30  
  Purchase #5 $240.55   4.652%   $251.7404   $251.74   $251.75   $251.70  
  Purchase #6 $8.81   6.117%   $9.3489   $9.35   $9.35   $9.30  
  Purchase #7 $41.78   3.470%   $43.2298   $43.23   $43.25   $43.20  
  7 purchase totals = $792.81       $845.6449   $845.65   $845.65   $845.60