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 $76.51   13.701%   $86.9926   $86.99   $87.00   $87.00  
  Purchase #2 $165.74   5.199%   $174.3568   $174.36   $174.35   $174.40  
  Purchase #3 $76.95   4.625%   $80.5089   $80.51   $80.50   $80.50  
  Purchase #4 $165.97   3.845%   $172.3515   $172.35   $172.35   $172.40  
  Purchase #5 $160.27   4.512%   $167.5014   $167.50   $167.50   $167.50  
  Purchase #6 $122.48   12.135%   $137.3429   $137.34   $137.35   $137.30  
  Purchase #7 $184.29   5.527%   $194.4757   $194.48   $194.50   $194.50  
  7 purchase totals = $952.21       $1,013.5298   $1,013.53   $1,013.55   $1,013.60