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 $184.59   12.208%   $207.1247   $207.12   $207.10   $207.10  
  Purchase #2 $54.86   5.660%   $57.9651   $57.97   $57.95   $58.00  
  Purchase #3 $68.62   3.427%   $70.9716   $70.97   $70.95   $71.00  
  Purchase #4 $241.68   12.853%   $272.7431   $272.74   $272.75   $272.70  
  Purchase #5 $144.72   11.642%   $161.5683   $161.57   $161.55   $161.60  
  Purchase #6 $235.43   4.500%   $246.0244   $246.02   $246.00   $246.00  
  Purchase #7 $132.36   9.597%   $145.0626   $145.06   $145.05   $145.10  
  7 purchase totals = $1,062.26       $1,161.4598   $1,161.45   $1,161.35   $1,161.50