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 $66.93   9.237%   $73.1123   $73.11   $73.10   $73.10  
  Purchase #2 $150.70   9.395%   $164.8583   $164.86   $164.85   $164.90  
  Purchase #3 $243.70   8.260%   $263.8296   $263.83   $263.85   $263.80  
  Purchase #4 $246.75   7.256%   $264.6542   $264.65   $264.65   $264.70  
  Purchase #5 $80.74   7.220%   $86.5694   $86.57   $86.55   $86.60  
  Purchase #6 $35.62   13.771%   $40.5252   $40.53   $40.55   $40.50  
  Purchase #7 $191.71   5.305%   $201.8802   $201.88   $201.90   $201.90  
  7 purchase totals = $1,016.15       $1,095.4292   $1,095.43   $1,095.45   $1,095.50