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 $188.47   11.677%   $210.4776   $210.48   $210.50   $210.50  
  Purchase #2 $86.43   7.626%   $93.0212   $93.02   $93.00   $93.00  
  Purchase #3 $230.30   3.115%   $237.4738   $237.47   $237.45   $237.50  
  Purchase #4 $40.50   5.365%   $42.6728   $42.67   $42.65   $42.70  
  Purchase #5 $165.98   9.391%   $181.5672   $181.57   $181.55   $181.60  
  Purchase #6 $245.86   9.360%   $268.8725   $268.87   $268.85   $268.90  
  Purchase #7 $37.45   10.370%   $41.3336   $41.33   $41.35   $41.30  
  7 purchase totals = $994.99       $1,075.4187   $1,075.41   $1,075.35   $1,075.50