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 $235.51   13.396%   $267.0589   $267.06   $267.05   $267.10  
  Purchase #2 $248.45   13.439%   $281.8392   $281.84   $281.85   $281.80  
  Purchase #3 $194.97   8.210%   $210.977   $210.98   $211.00   $211.00  
  Purchase #4 $86.79   4.281%   $90.5055   $90.51   $90.50   $90.50  
  Purchase #5 $202.25   5.222%   $212.8115   $212.81   $212.80   $212.80  
  Purchase #6 $169.30   7.139%   $181.3863   $181.39   $181.40   $181.40  
  Purchase #7 $44.33   11.354%   $49.3632   $49.36   $49.35   $49.40  
  7 purchase totals = $1,181.60       $1,293.9416   $1,293.95   $1,293.95   $1,294.00