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 $128.48   11.540%   $143.3066   $143.31   $143.30   $143.30  
  Purchase #2 $216.41   11.281%   $240.8232   $240.82   $240.80   $240.80  
  Purchase #3 $29.84   9.573%   $32.6966   $32.70   $32.70   $32.70  
  Purchase #4 $6.26   11.694%   $6.992   $6.99   $7.00   $7.00  
  Purchase #5 $115.32   4.235%   $120.2038   $120.20   $120.20   $120.20  
  Purchase #6 $77.53   9.745%   $85.0853   $85.09   $85.10   $85.10  
  Purchase #7 $64.92   10.590%   $71.795   $71.80   $71.80   $71.80  
  7 purchase totals = $638.76       $700.9025   $700.91   $700.90   $700.90