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 $84.33   11.707%   $94.2025   $94.20   $94.20   $94.20  
  Purchase #2 $150.52   8.213%   $162.8822   $162.88   $162.90   $162.90  
  Purchase #3 $32.46   7.538%   $34.9068   $34.91   $34.90   $34.90  
  Purchase #4 $181.43   11.236%   $201.8155   $201.82   $201.80   $201.80  
  Purchase #5 $212.73   6.555%   $226.6745   $226.67   $226.65   $226.70  
  Purchase #6 $182.33   4.578%   $190.6771   $190.68   $190.70   $190.70  
  Purchase #7 $130.99   6.820%   $139.9235   $139.92   $139.90   $139.90  
  7 purchase totals = $974.79       $1,051.0821   $1,051.08   $1,051.05   $1,051.10