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 $213.49   8.718%   $232.1021   $232.10   $232.10   $232.10  
  Purchase #2 $139.40   5.764%   $147.435   $147.44   $147.45   $147.40  
  Purchase #3 $109.63   11.140%   $121.8428   $121.84   $121.85   $121.80  
  Purchase #4 $26.27   9.460%   $28.7551   $28.76   $28.75   $28.80  
  Purchase #5 $12.37   6.180%   $13.1345   $13.13   $13.15   $13.10  
  Purchase #6 $134.83   12.852%   $152.1584   $152.16   $152.15   $152.20  
  Purchase #7 $36.28   7.818%   $39.1164   $39.12   $39.10   $39.10  
  7 purchase totals = $672.27       $734.5443   $734.55   $734.55   $734.50