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 $140.45   6.835%   $150.0498   $150.05   $150.05   $150.00  
  Purchase #2 $58.27   4.472%   $60.8758   $60.88   $60.90   $60.90  
  Purchase #3 $116.58   4.667%   $122.0208   $122.02   $122.00   $122.00  
  Purchase #4 $182.28   13.721%   $207.2906   $207.29   $207.30   $207.30  
  Purchase #5 $189.81   12.522%   $213.578   $213.58   $213.60   $213.60  
  Purchase #6 $120.44   12.343%   $135.3059   $135.31   $135.30   $135.30  
  Purchase #7 $145.43   4.585%   $152.098   $152.10   $152.10   $152.10  
  7 purchase totals = $953.26       $1,041.2189   $1,041.23   $1,041.25   $1,041.20