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 $53.96   5.679%   $57.0244   $57.02   $57.00   $57.00  
  Purchase #2 $134.65   8.414%   $145.9795   $145.98   $146.00   $146.00  
  Purchase #3 $35.52   6.188%   $37.718   $37.72   $37.70   $37.70  
  Purchase #4 $240.65   12.643%   $271.0754   $271.08   $271.10   $271.10  
  Purchase #5 $186.40   10.133%   $205.2879   $205.29   $205.30   $205.30  
  Purchase #6 $192.88   6.844%   $206.0807   $206.08   $206.10   $206.10  
  Purchase #7 $178.90   10.110%   $196.9868   $196.99   $197.00   $197.00  
  7 purchase totals = $1,022.96       $1,120.1527   $1,120.16   $1,120.20   $1,120.20