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 $59.40   3.643%   $61.5639   $61.56   $61.55   $61.60  
  Purchase #2 $150.49   9.751%   $165.1643   $165.16   $165.15   $165.20  
  Purchase #3 $210.67   12.350%   $236.6877   $236.69   $236.70   $236.70  
  Purchase #4 $224.74   6.331%   $238.9683   $238.97   $238.95   $239.00  
  Purchase #5 $239.48   9.818%   $262.9921   $262.99   $263.00   $263.00  
  Purchase #6 $85.42   9.467%   $93.5067   $93.51   $93.50   $93.50  
  Purchase #7 $157.81   4.421%   $164.7868   $164.79   $164.80   $164.80  
  7 purchase totals = $1,128.01       $1,223.6698   $1,223.67   $1,223.65   $1,223.80