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 $62.56   12.261%   $70.2305   $70.23   $70.25   $70.20  
  Purchase #2 $220.33   11.133%   $244.8593   $244.86   $244.85   $244.90  
  Purchase #3 $43.99   6.819%   $46.9897   $46.99   $47.00   $47.00  
  Purchase #4 $189.74   11.493%   $211.5468   $211.55   $211.55   $211.50  
  Purchase #5 $134.34   5.688%   $141.9813   $141.98   $142.00   $142.00  
  Purchase #6 $240.95   7.487%   $258.9899   $258.99   $259.00   $259.00  
  Purchase #7 $225.95   5.644%   $238.7026   $238.70   $238.70   $238.70  
  7 purchase totals = $1,117.86       $1,213.3001   $1,213.30   $1,213.35   $1,213.30