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 $134.27   5.543%   $141.7126   $141.71   $141.70   $141.70  
  Purchase #2 $224.52   8.322%   $243.2046   $243.20   $243.20   $243.20  
  Purchase #3 $236.38   13.106%   $267.36   $267.36   $267.35   $267.40  
  Purchase #4 $46.56   7.419%   $50.0143   $50.01   $50.00   $50.00  
  Purchase #5 $49.36   13.159%   $55.8553   $55.86   $55.85   $55.90  
  Purchase #6 $202.33   3.378%   $209.1647   $209.16   $209.15   $209.20  
  Purchase #7 $52.91   12.112%   $59.3185   $59.32   $59.30   $59.30  
  7 purchase totals = $946.33       $1,026.6300   $1,026.62   $1,026.55   $1,026.70