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 $168.54   5.207%   $177.3159   $177.32   $177.30   $177.30  
  Purchase #2 $117.51   5.533%   $124.0118   $124.01   $124.00   $124.00  
  Purchase #3 $110.83   11.136%   $123.172   $123.17   $123.15   $123.20  
  Purchase #4 $49.71   9.217%   $54.2918   $54.29   $54.30   $54.30  
  Purchase #5 $11.79   6.620%   $12.5705   $12.57   $12.55   $12.60  
  Purchase #6 $157.25   10.811%   $174.2503   $174.25   $174.25   $174.30  
  Purchase #7 $29.68   6.416%   $31.5843   $31.58   $31.60   $31.60  
  7 purchase totals = $645.31       $697.1966   $697.19   $697.15   $697.30