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 $139.44   10.569%   $154.1774   $154.18   $154.20   $154.20  
  Purchase #2 $134.86   10.562%   $149.1039   $149.10   $149.10   $149.10  
  Purchase #3 $86.65   7.783%   $93.394   $93.39   $93.40   $93.40  
  Purchase #4 $54.95   12.843%   $62.0072   $62.01   $62.00   $62.00  
  Purchase #5 $219.57   3.205%   $226.6072   $226.61   $226.60   $226.60  
  Purchase #6 $227.43   12.392%   $255.6131   $255.61   $255.60   $255.60  
  Purchase #7 $239.83   3.774%   $248.8812   $248.88   $248.90   $248.90  
  7 purchase totals = $1,102.73       $1,189.7840   $1,189.78   $1,189.80   $1,189.80