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 $33.98   5.138%   $35.7259   $35.73   $35.75   $35.70  
  Purchase #2 $120.42   10.379%   $132.9184   $132.92   $132.90   $132.90  
  Purchase #3 $134.77   7.436%   $144.7915   $144.79   $144.80   $144.80  
  Purchase #4 $174.34   4.148%   $181.5716   $181.57   $181.55   $181.60  
  Purchase #5 $229.26   8.810%   $249.4578   $249.46   $249.45   $249.50  
  Purchase #6 $234.27   11.354%   $260.869   $260.87   $260.85   $260.90  
  Purchase #7 $196.41   5.145%   $206.5153   $206.52   $206.50   $206.50  
  7 purchase totals = $1,123.45       $1,211.8495   $1,211.86   $1,211.80   $1,211.90