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 $10.84   11.740%   $12.1126   $12.11   $12.10   $12.10  
  Purchase #2 $64.94   10.685%   $71.8788   $71.88   $71.90   $71.90  
  Purchase #3 $191.98   7.790%   $206.9352   $206.94   $206.95   $206.90  
  Purchase #4 $230.54   6.809%   $246.2375   $246.24   $246.25   $246.20  
  Purchase #5 $218.37   12.203%   $245.0177   $245.02   $245.00   $245.00  
  Purchase #6 $120.41   4.434%   $125.749   $125.75   $125.75   $125.70  
  Purchase #7 $143.64   6.109%   $152.415   $152.42   $152.40   $152.40  
  7 purchase totals = $980.72       $1,060.3458   $1,060.36   $1,060.35   $1,060.20