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 $53.33   6.614%   $56.8572   $56.86   $56.85   $56.90  
  Purchase #2 $194.41   5.715%   $205.5205   $205.52   $205.50   $205.50  
  Purchase #3 $167.54   8.196%   $181.2716   $181.27   $181.25   $181.30  
  Purchase #4 $211.60   13.739%   $240.6717   $240.67   $240.65   $240.70  
  Purchase #5 $112.84   6.855%   $120.5752   $120.58   $120.60   $120.60  
  Purchase #6 $138.45   11.484%   $154.3496   $154.35   $154.35   $154.30  
  Purchase #7 $187.70   10.418%   $207.2546   $207.25   $207.25   $207.30  
  7 purchase totals = $1,065.87       $1,166.5004   $1,166.50   $1,166.45   $1,166.60