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 $45.86   11.251%   $51.0197   $51.02   $51.00   $51.00  
  Purchase #2 $160.58   11.166%   $178.5104   $178.51   $178.50   $178.50  
  Purchase #3 $244.40   5.839%   $258.6705   $258.67   $258.65   $258.70  
  Purchase #4 $87.45   12.394%   $98.2886   $98.29   $98.30   $98.30  
  Purchase #5 $249.90   9.113%   $272.6734   $272.67   $272.65   $272.70  
  Purchase #6 $79.79   3.747%   $82.7797   $82.78   $82.80   $82.80  
  Purchase #7 $49.86   7.544%   $53.6214   $53.62   $53.60   $53.60  
  7 purchase totals = $917.84       $995.5637   $995.56   $995.50   $995.60