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 $84.26   13.762%   $95.8559   $95.86   $95.85   $95.90  
  Purchase #2 $181.26   6.469%   $192.9857   $192.99   $193.00   $193.00  
  Purchase #3 $130.93   12.404%   $147.1706   $147.17   $147.15   $147.20  
  Purchase #4 $94.38   5.740%   $99.7974   $99.80   $99.80   $99.80  
  Purchase #5 $190.76   5.847%   $201.9137   $201.91   $201.90   $201.90  
  Purchase #6 $120.47   6.623%   $128.4487   $128.45   $128.45   $128.40  
  Purchase #7 $139.69   5.404%   $147.2388   $147.24   $147.25   $147.20  
  7 purchase totals = $941.75       $1,013.4108   $1,013.42   $1,013.40   $1,013.40