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 $124.76   10.573%   $137.9509   $137.95   $137.95   $138.00  
  Purchase #2 $124.65   10.156%   $137.3095   $137.31   $137.30   $137.30  
  Purchase #3 $54.49   8.597%   $59.1745   $59.17   $59.15   $59.20  
  Purchase #4 $59.25   13.112%   $67.0189   $67.02   $67.00   $67.00  
  Purchase #5 $231.99   9.241%   $253.4282   $253.43   $253.45   $253.40  
  Purchase #6 $105.52   7.200%   $113.1174   $113.12   $113.10   $113.10  
  Purchase #7 $180.45   5.757%   $190.8385   $190.84   $190.85   $190.80  
  7 purchase totals = $881.11       $958.8379   $958.84   $958.80   $958.80