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 $171.95   13.267%   $194.7626   $194.76   $194.75   $194.80  
  Purchase #2 $49.91   12.837%   $56.3169   $56.32   $56.30   $56.30  
  Purchase #3 $129.66   5.461%   $136.7407   $136.74   $136.75   $136.70  
  Purchase #4 $82.49   9.797%   $90.5715   $90.57   $90.55   $90.60  
  Purchase #5 $211.93   5.424%   $223.4251   $223.43   $223.45   $223.40  
  Purchase #6 $65.58   13.449%   $74.3999   $74.40   $74.40   $74.40  
  Purchase #7 $203.52   10.115%   $224.106   $224.11   $224.10   $224.10  
  7 purchase totals = $915.04       $1,000.3227   $1,000.33   $1,000.30   $1,000.30