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 $34.44   3.157%   $35.5273   $35.53   $35.55   $35.50  
  Purchase #2 $160.87   11.485%   $179.3459   $179.35   $179.35   $179.30  
  Purchase #3 $156.95   6.853%   $167.7058   $167.71   $167.70   $167.70  
  Purchase #4 $61.64   5.592%   $65.0869   $65.09   $65.10   $65.10  
  Purchase #5 $225.42   3.803%   $233.9927   $233.99   $234.00   $234.00  
  Purchase #6 $119.90   10.625%   $132.6394   $132.64   $132.65   $132.60  
  Purchase #7 $187.83   5.464%   $198.093   $198.09   $198.10   $198.10  
  7 purchase totals = $947.05       $1,012.3910   $1,012.40   $1,012.45   $1,012.30