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 $59.98   4.435%   $62.6401   $62.64   $62.65   $62.60  
  Purchase #2 $23.55   8.581%   $25.5708   $25.57   $25.55   $25.60  
  Purchase #3 $228.28   5.478%   $240.7852   $240.79   $240.80   $240.80  
  Purchase #4 $50.76   12.219%   $56.9624   $56.96   $56.95   $57.00  
  Purchase #5 $130.91   11.778%   $146.3286   $146.33   $146.35   $146.30  
  Purchase #6 $165.52   4.709%   $173.3143   $173.31   $173.30   $173.30  
  Purchase #7 $27.40   10.390%   $30.2469   $30.25   $30.25   $30.20  
  7 purchase totals = $686.40       $735.8483   $735.85   $735.85   $735.80