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 $66.97   6.270%   $71.169   $71.17   $71.15   $71.20  
  Purchase #2 $207.83   3.740%   $215.6028   $215.60   $215.60   $215.60  
  Purchase #3 $46.27   13.629%   $52.5761   $52.58   $52.60   $52.60  
  Purchase #4 $134.38   8.187%   $145.3817   $145.38   $145.40   $145.40  
  Purchase #5 $211.29   9.238%   $230.809   $230.81   $230.80   $230.80  
  Purchase #6 $200.66   3.370%   $207.4222   $207.42   $207.40   $207.40  
  Purchase #7 $128.56   8.835%   $139.9183   $139.92   $139.90   $139.90  
  7 purchase totals = $995.96       $1,062.8791   $1,062.88   $1,062.85   $1,062.90