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 $29.81   11.351%   $33.1937   $33.19   $33.20   $33.20  
  Purchase #2 $129.45   7.764%   $139.5005   $139.50   $139.50   $139.50  
  Purchase #3 $190.32   6.413%   $202.5252   $202.53   $202.55   $202.50  
  Purchase #4 $238.29   6.508%   $253.7979   $253.80   $253.80   $253.80  
  Purchase #5 $73.63   9.333%   $80.5019   $80.50   $80.50   $80.50  
  Purchase #6 $215.26   9.529%   $235.7721   $235.77   $235.75   $235.80  
  Purchase #7 $77.64   11.401%   $86.4917   $86.49   $86.50   $86.50  
  7 purchase totals = $954.40       $1,031.7830   $1,031.78   $1,031.80   $1,031.80