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 $184.78   10.137%   $203.5111   $203.51   $203.50   $203.50  
  Purchase #2 $10.29   7.346%   $11.0459   $11.05   $11.05   $11.00  
  Purchase #3 $178.58   4.844%   $187.2304   $187.23   $187.25   $187.20  
  Purchase #4 $238.57   10.449%   $263.4982   $263.50   $263.50   $263.50  
  Purchase #5 $224.79   12.251%   $252.329   $252.33   $252.35   $252.30  
  Purchase #6 $210.87   3.719%   $218.7123   $218.71   $218.70   $218.70  
  Purchase #7 $59.92   6.511%   $63.8214   $63.82   $63.80   $63.80  
  7 purchase totals = $1,107.80       $1,200.1483   $1,200.15   $1,200.15   $1,200.00