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 $41.86   3.574%   $43.3561   $43.36   $43.35   $43.40  
  Purchase #2 $137.43   13.803%   $156.3995   $156.40   $156.40   $156.40  
  Purchase #3 $132.56   4.171%   $138.0891   $138.09   $138.10   $138.10  
  Purchase #4 $180.68   13.224%   $204.5731   $204.57   $204.55   $204.60  
  Purchase #5 $239.47   4.682%   $250.682   $250.68   $250.70   $250.70  
  Purchase #6 $138.30   9.564%   $151.527   $151.53   $151.55   $151.50  
  Purchase #7 $141.40   4.297%   $147.476   $147.48   $147.50   $147.50  
  7 purchase totals = $1,011.70       $1,092.1028   $1,092.11   $1,092.15   $1,092.20