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 $56.90   13.484%   $64.5724   $64.57   $64.55   $64.60  
  Purchase #2 $192.60   6.651%   $205.4098   $205.41   $205.40   $205.40  
  Purchase #3 $31.89   3.713%   $33.0741   $33.07   $33.05   $33.10  
  Purchase #4 $165.78   11.163%   $184.286   $184.29   $184.30   $184.30  
  Purchase #5 $57.44   11.629%   $64.1197   $64.12   $64.10   $64.10  
  Purchase #6 $91.69   8.330%   $99.3278   $99.33   $99.35   $99.30  
  Purchase #7 $110.29   10.869%   $122.2774   $122.28   $122.30   $122.30  
  7 purchase totals = $706.59       $773.0672   $773.07   $773.05   $773.10