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 $176.83   3.333%   $182.7237   $182.72   $182.70   $182.70  
  Purchase #2 $151.91   10.302%   $167.5598   $167.56   $167.55   $167.60  
  Purchase #3 $204.95   10.212%   $225.8795   $225.88   $225.90   $225.90  
  Purchase #4 $62.32   10.244%   $68.7041   $68.70   $68.70   $68.70  
  Purchase #5 $82.43   13.347%   $93.4319   $93.43   $93.45   $93.40  
  Purchase #6 $181.80   11.114%   $202.0053   $202.01   $202.00   $202.00  
  Purchase #7 $113.94   3.209%   $117.5963   $117.60   $117.60   $117.60  
  7 purchase totals = $974.18       $1,057.9006   $1,057.90   $1,057.90   $1,057.90