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 $106.70   6.804%   $113.9599   $113.96   $113.95   $114.00  
  Purchase #2 $146.80   5.838%   $155.3702   $155.37   $155.35   $155.40  
  Purchase #3 $181.71   11.644%   $202.8683   $202.87   $202.85   $202.90  
  Purchase #4 $58.52   9.627%   $64.1537   $64.15   $64.15   $64.20  
  Purchase #5 $25.36   6.295%   $26.9564   $26.96   $26.95   $27.00  
  Purchase #6 $58.48   8.874%   $63.6695   $63.67   $63.65   $63.70  
  Purchase #7 $44.74   6.810%   $47.7868   $47.79   $47.80   $47.80  
  7 purchase totals = $622.31       $674.7648   $674.77   $674.70   $675.00