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 $73.27   10.212%   $80.7523   $80.75   $80.75   $80.80  
  Purchase #2 $232.95   11.607%   $259.9885   $259.99   $260.00   $260.00  
  Purchase #3 $186.99   10.445%   $206.5211   $206.52   $206.50   $206.50  
  Purchase #4 $17.79   10.457%   $19.6503   $19.65   $19.65   $19.70  
  Purchase #5 $120.66   5.658%   $127.4869   $127.49   $127.50   $127.50  
  Purchase #6 $142.40   3.188%   $146.9397   $146.94   $146.95   $146.90  
  Purchase #7 $159.38   11.250%   $177.3103   $177.31   $177.30   $177.30  
  7 purchase totals = $933.44       $1,018.6491   $1,018.65   $1,018.65   $1,018.70