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 $188.54   12.316%   $211.7606   $211.76   $211.75   $211.80  
  Purchase #2 $156.54   5.307%   $164.8476   $164.85   $164.85   $164.80  
  Purchase #3 $67.50   6.335%   $71.7761   $71.78   $71.80   $71.80  
  Purchase #4 $191.35   11.693%   $213.7246   $213.72   $213.70   $213.70  
  Purchase #5 $23.79   13.199%   $26.93   $26.93   $26.95   $26.90  
  Purchase #6 $196.53   11.790%   $219.7009   $219.70   $219.70   $219.70  
  Purchase #7 $171.31   12.834%   $193.2959   $193.30   $193.30   $193.30  
  7 purchase totals = $995.56       $1,102.0357   $1,102.04   $1,102.05   $1,102.00