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 $93.56   10.695%   $103.5662   $103.57   $103.55   $103.60  
  Purchase #2 $232.32   8.124%   $251.1937   $251.19   $251.20   $251.20  
  Purchase #3 $48.72   7.306%   $52.2795   $52.28   $52.30   $52.30  
  Purchase #4 $210.30   10.394%   $232.1586   $232.16   $232.15   $232.20  
  Purchase #5 $204.45   12.658%   $230.3293   $230.33   $230.35   $230.30  
  Purchase #6 $117.61   12.242%   $132.0078   $132.01   $132.00   $132.00  
  Purchase #7 $9.86   12.447%   $11.0873   $11.09   $11.10   $11.10  
  7 purchase totals = $916.82       $1,012.6224   $1,012.63   $1,012.65   $1,012.70