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 $210.87   12.166%   $236.5244   $236.52   $236.50   $236.50  
  Purchase #2 $206.58   6.666%   $220.3506   $220.35   $220.35   $220.40  
  Purchase #3 $100.83   6.115%   $106.9958   $107.00   $107.00   $107.00  
  Purchase #4 $198.42   6.728%   $211.7697   $211.77   $211.75   $211.80  
  Purchase #5 $57.80   9.710%   $63.4124   $63.41   $63.40   $63.40  
  Purchase #6 $38.79   11.320%   $43.181   $43.18   $43.20   $43.20  
  Purchase #7 $81.66   3.862%   $84.8137   $84.81   $84.80   $84.80  
  7 purchase totals = $894.95       $967.0476   $967.04   $967.00   $967.10