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 $32.55   7.570%   $35.014   $35.01   $35.00   $35.00  
  Purchase #2 $15.40   13.767%   $17.5201   $17.52   $17.50   $17.50  
  Purchase #3 $178.36   13.192%   $201.8893   $201.89   $201.90   $201.90  
  Purchase #4 $212.96   12.346%   $239.252   $239.25   $239.25   $239.30  
  Purchase #5 $53.79   4.666%   $56.2998   $56.30   $56.30   $56.30  
  Purchase #6 $189.36   11.729%   $211.57   $211.57   $211.55   $211.60  
  Purchase #7 $112.89   9.680%   $123.8178   $123.82   $123.80   $123.80  
  7 purchase totals = $795.31       $885.3630   $885.36   $885.30   $885.40