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 $179.41   13.457%   $203.5532   $203.55   $203.55   $203.60  
  Purchase #2 $131.58   8.606%   $142.9038   $142.90   $142.90   $142.90  
  Purchase #3 $180.79   6.741%   $192.9771   $192.98   $193.00   $193.00  
  Purchase #4 $225.70   8.743%   $245.433   $245.43   $245.45   $245.40  
  Purchase #5 $213.31   6.140%   $226.4072   $226.41   $226.40   $226.40  
  Purchase #6 $40.74   11.604%   $45.4675   $45.47   $45.45   $45.50  
  Purchase #7 $149.82   8.270%   $162.2101   $162.21   $162.20   $162.20  
  7 purchase totals = $1,121.35       $1,218.9519   $1,218.95   $1,218.95   $1,219.00