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 $136.75   6.532%   $145.6825   $145.68   $145.70   $145.70  
  Purchase #2 $53.45   3.510%   $55.3261   $55.33   $55.35   $55.30  
  Purchase #3 $142.88   11.812%   $159.757   $159.76   $159.75   $159.80  
  Purchase #4 $81.76   6.538%   $87.1055   $87.11   $87.10   $87.10  
  Purchase #5 $124.68   7.717%   $134.3016   $134.30   $134.30   $134.30  
  Purchase #6 $224.41   5.174%   $236.021   $236.02   $236.00   $236.00  
  Purchase #7 $185.54   4.861%   $194.5591   $194.56   $194.55   $194.60  
  7 purchase totals = $949.47       $1,012.7528   $1,012.76   $1,012.75   $1,012.80