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 $24.91   10.640%   $27.5604   $27.56   $27.55   $27.60  
  Purchase #2 $187.88   13.370%   $212.9996   $213.00   $213.00   $213.00  
  Purchase #3 $149.95   12.141%   $168.1554   $168.16   $168.15   $168.20  
  Purchase #4 $171.96   7.108%   $184.1829   $184.18   $184.20   $184.20  
  Purchase #5 $200.94   11.329%   $223.7045   $223.70   $223.70   $223.70  
  Purchase #6 $235.84   3.591%   $244.309   $244.31   $244.30   $244.30  
  Purchase #7 $195.38   13.160%   $221.092   $221.09   $221.10   $221.10  
  7 purchase totals = $1,166.86       $1,282.0038   $1,282.00   $1,282.00   $1,282.10