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 $31.67   13.173%   $35.8419   $35.84   $35.85   $35.80  
  Purchase #2 $250.94   7.179%   $268.955   $268.96   $268.95   $269.00  
  Purchase #3 $23.53   9.790%   $25.8336   $25.83   $25.85   $25.80  
  Purchase #4 $211.30   6.255%   $224.5168   $224.52   $224.50   $224.50  
  Purchase #5 $85.37   4.381%   $89.1101   $89.11   $89.10   $89.10  
  Purchase #6 $38.87   12.414%   $43.6953   $43.70   $43.70   $43.70  
  Purchase #7 $233.58   10.486%   $258.0732   $258.07   $258.05   $258.10  
  7 purchase totals = $875.26       $946.0259   $946.03   $946.00   $946.00