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 $155.98   12.324%   $175.203   $175.20   $175.20   $175.20  
  Purchase #2 $74.37   4.717%   $77.878   $77.88   $77.90   $77.90  
  Purchase #3 $201.68   7.267%   $216.3361   $216.34   $216.35   $216.30  
  Purchase #4 $64.34   9.774%   $70.6286   $70.63   $70.65   $70.60  
  Purchase #5 $207.48   5.258%   $218.3893   $218.39   $218.40   $218.40  
  Purchase #6 $199.87   5.839%   $211.5404   $211.54   $211.55   $211.50  
  Purchase #7 $135.31   8.104%   $146.2755   $146.28   $146.30   $146.30  
  7 purchase totals = $1,039.03       $1,116.2509   $1,116.26   $1,116.35   $1,116.20