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 $34.82   7.670%   $37.4907   $37.49   $37.50   $37.50  
  Purchase #2 $188.40   7.663%   $202.8371   $202.84   $202.85   $202.80  
  Purchase #3 $59.95   3.700%   $62.1682   $62.17   $62.15   $62.20  
  Purchase #4 $123.91   5.107%   $130.2381   $130.24   $130.25   $130.20  
  Purchase #5 $242.31   13.665%   $275.4217   $275.42   $275.40   $275.40  
  Purchase #6 $108.77   3.102%   $112.144   $112.14   $112.15   $112.10  
  Purchase #7 $179.65   12.151%   $201.4793   $201.48   $201.50   $201.50  
  7 purchase totals = $937.81       $1,021.7791   $1,021.78   $1,021.80   $1,021.70