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 $110.59   8.483%   $119.9713   $119.97   $119.95   $120.00  
  Purchase #2 $234.41   11.847%   $262.1806   $262.18   $262.20   $262.20  
  Purchase #3 $39.95   3.784%   $41.4617   $41.46   $41.45   $41.50  
  Purchase #4 $186.65   8.564%   $202.6347   $202.63   $202.65   $202.60  
  Purchase #5 $180.27   6.133%   $191.326   $191.33   $191.35   $191.30  
  Purchase #6 $11.98   11.415%   $13.3475   $13.35   $13.35   $13.30  
  Purchase #7 $187.30   6.173%   $198.862   $198.86   $198.85   $198.90  
  7 purchase totals = $951.15       $1,029.7838   $1,029.78   $1,029.80   $1,029.80