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 $243.77   8.328%   $264.0712   $264.07   $264.05   $264.10  
  Purchase #2 $196.94   10.469%   $217.5576   $217.56   $217.55   $217.60  
  Purchase #3 $86.99   9.278%   $95.0609   $95.06   $95.05   $95.10  
  Purchase #4 $54.84   6.601%   $58.46   $58.46   $58.45   $58.50  
  Purchase #5 $12.53   7.589%   $13.4809   $13.48   $13.50   $13.50  
  Purchase #6 $232.79   11.105%   $258.6413   $258.64   $258.65   $258.60  
  Purchase #7 $170.29   8.502%   $184.7681   $184.77   $184.75   $184.80  
  7 purchase totals = $998.15       $1,092.0400   $1,092.04   $1,092.00   $1,092.20