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 $147.86   10.451%   $163.3128   $163.31   $163.30   $163.30  
  Purchase #2 $165.85   8.141%   $179.3518   $179.35   $179.35   $179.40  
  Purchase #3 $139.37   10.339%   $153.7795   $153.78   $153.80   $153.80  
  Purchase #4 $100.35   12.121%   $112.5134   $112.51   $112.50   $112.50  
  Purchase #5 $52.91   5.764%   $55.9597   $55.96   $55.95   $56.00  
  Purchase #6 $73.52   3.530%   $76.1153   $76.12   $76.10   $76.10  
  Purchase #7 $126.59   4.725%   $132.5714   $132.57   $132.55   $132.60  
  7 purchase totals = $806.45       $873.6039   $873.60   $873.55   $873.70