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 $61.56   6.265%   $65.4167   $65.42   $65.40   $65.40  
  Purchase #2 $191.36   10.656%   $211.7513   $211.75   $211.75   $211.80  
  Purchase #3 $187.82   4.169%   $195.6502   $195.65   $195.65   $195.70  
  Purchase #4 $173.57   13.195%   $196.4726   $196.47   $196.45   $196.50  
  Purchase #5 $157.45   6.558%   $167.7756   $167.78   $167.80   $167.80  
  Purchase #6 $32.64   12.344%   $36.6691   $36.67   $36.65   $36.70  
  Purchase #7 $184.27   10.714%   $204.0127   $204.01   $204.00   $204.00  
  7 purchase totals = $988.67       $1,077.7482   $1,077.75   $1,077.70   $1,077.90