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 $61.26   5.318%   $64.5178   $64.52   $64.50   $64.50  
  Purchase #2 $59.55   8.449%   $64.5814   $64.58   $64.60   $64.60  
  Purchase #3 $122.66   5.373%   $129.2505   $129.25   $129.25   $129.30  
  Purchase #4 $45.94   8.224%   $49.7181   $49.72   $49.70   $49.70  
  Purchase #5 $99.86   6.453%   $106.304   $106.30   $106.30   $106.30  
  Purchase #6 $225.31   11.781%   $251.8538   $251.85   $251.85   $251.90  
  Purchase #7 $210.60   9.396%   $230.388   $230.39   $230.40   $230.40  
  7 purchase totals = $825.18       $896.6136   $896.61   $896.60   $896.70