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 $173.39   12.632%   $195.2926   $195.29   $195.30   $195.30  
  Purchase #2 $149.60   4.849%   $156.8541   $156.85   $156.85   $156.90  
  Purchase #3 $102.62   5.776%   $108.5473   $108.55   $108.55   $108.50  
  Purchase #4 $133.64   3.792%   $138.7076   $138.71   $138.70   $138.70  
  Purchase #5 $167.56   11.484%   $186.8026   $186.80   $186.80   $186.80  
  Purchase #6 $65.72   13.397%   $74.5245   $74.52   $74.50   $74.50  
  Purchase #7 $174.69   13.107%   $197.5866   $197.59   $197.60   $197.60  
  7 purchase totals = $967.22       $1,058.3153   $1,058.31   $1,058.30   $1,058.30