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 $62.63   7.660%   $67.4275   $67.43   $67.45   $67.40  
  Purchase #2 $172.68   6.684%   $184.2219   $184.22   $184.20   $184.20  
  Purchase #3 $57.49   4.542%   $60.1012   $60.10   $60.10   $60.10  
  Purchase #4 $229.53   9.182%   $250.6054   $250.61   $250.60   $250.60  
  Purchase #5 $93.98   12.871%   $106.0762   $106.08   $106.10   $106.10  
  Purchase #6 $233.68   5.132%   $245.6725   $245.67   $245.65   $245.70  
  Purchase #7 $118.57   3.409%   $122.6121   $122.61   $122.60   $122.60  
  7 purchase totals = $968.56       $1,036.7168   $1,036.72   $1,036.70   $1,036.70