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 $245.93   5.452%   $259.3381   $259.34   $259.35   $259.30  
  Purchase #2 $147.52   5.374%   $155.4477   $155.45   $155.45   $155.40  
  Purchase #3 $137.94   8.272%   $149.3504   $149.35   $149.35   $149.40  
  Purchase #4 $21.80   13.156%   $24.668   $24.67   $24.65   $24.70  
  Purchase #5 $52.50   12.387%   $59.0032   $59.00   $59.00   $59.00  
  Purchase #6 $228.64   5.273%   $240.6962   $240.70   $240.70   $240.70  
  Purchase #7 $227.65   3.456%   $235.5176   $235.52   $235.50   $235.50  
  7 purchase totals = $1,061.98       $1,124.0212   $1,124.03   $1,124.00   $1,124.00