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 $213.98   8.492%   $232.1512   $232.15   $232.15   $232.20  
  Purchase #2 $41.27   8.193%   $44.6513   $44.65   $44.65   $44.70  
  Purchase #3 $223.96   12.677%   $252.3514   $252.35   $252.35   $252.40  
  Purchase #4 $24.53   3.460%   $25.3787   $25.38   $25.40   $25.40  
  Purchase #5 $193.47   4.462%   $202.1026   $202.10   $202.10   $202.10  
  Purchase #6 $249.45   9.389%   $272.8709   $272.87   $272.85   $272.90  
  Purchase #7 $29.93   7.146%   $32.0688   $32.07   $32.05   $32.10  
  7 purchase totals = $976.59       $1,061.5749   $1,061.57   $1,061.55   $1,061.80