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 $176.79   13.459%   $200.5842   $200.58   $200.60   $200.60  
  Purchase #2 $96.46   11.483%   $107.5365   $107.54   $107.55   $107.50  
  Purchase #3 $119.29   8.781%   $129.7649   $129.76   $129.75   $129.80  
  Purchase #4 $177.39   7.809%   $191.2424   $191.24   $191.25   $191.20  
  Purchase #5 $40.31   5.477%   $42.5178   $42.52   $42.50   $42.50  
  Purchase #6 $42.54   3.376%   $43.9762   $43.98   $44.00   $44.00  
  Purchase #7 $220.47   5.718%   $233.0765   $233.08   $233.10   $233.10  
  7 purchase totals = $873.25       $948.6985   $948.70   $948.75   $948.70