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 $198.52   6.657%   $211.7355   $211.74   $211.75   $211.70  
  Purchase #2 $144.72   13.550%   $164.3296   $164.33   $164.35   $164.30  
  Purchase #3 $57.42   13.819%   $65.3549   $65.35   $65.35   $65.40  
  Purchase #4 $173.29   3.809%   $179.8906   $179.89   $179.90   $179.90  
  Purchase #5 $84.91   10.425%   $93.7619   $93.76   $93.75   $93.80  
  Purchase #6 $151.80   11.744%   $169.6274   $169.63   $169.65   $169.60  
  Purchase #7 $159.79   7.433%   $171.6672   $171.67   $171.65   $171.70  
  7 purchase totals = $970.45       $1,056.3671   $1,056.37   $1,056.40   $1,056.40