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 $106.82   4.395%   $111.5147   $111.51   $111.50   $111.50  
  Purchase #2 $46.98   11.801%   $52.5241   $52.52   $52.50   $52.50  
  Purchase #3 $34.47   7.653%   $37.108   $37.11   $37.10   $37.10  
  Purchase #4 $97.85   11.690%   $109.2887   $109.29   $109.30   $109.30  
  Purchase #5 $152.31   11.151%   $169.2941   $169.29   $169.30   $169.30  
  Purchase #6 $57.63   6.408%   $61.3229   $61.32   $61.30   $61.30  
  Purchase #7 $152.50   9.301%   $166.684   $166.68   $166.70   $166.70  
  7 purchase totals = $648.56       $707.7365   $707.72   $707.70   $707.70