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 $213.82   6.149%   $226.9678   $226.97   $226.95   $227.00  
  Purchase #2 $173.97   5.729%   $183.9367   $183.94   $183.95   $183.90  
  Purchase #3 $104.53   13.270%   $118.4011   $118.40   $118.40   $118.40  
  Purchase #4 $147.43   5.758%   $155.919   $155.92   $155.90   $155.90  
  Purchase #5 $114.69   13.419%   $130.0803   $130.08   $130.10   $130.10  
  Purchase #6 $20.57   7.171%   $22.0451   $22.05   $22.05   $22.00  
  Purchase #7 $52.93   12.857%   $59.7352   $59.74   $59.75   $59.70  
  7 purchase totals = $827.94       $897.0852   $897.10   $897.10   $897.00