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 $41.34   12.122%   $46.3512   $46.35   $46.35   $46.40  
  Purchase #2 $53.74   7.269%   $57.6464   $57.65   $57.65   $57.60  
  Purchase #3 $55.44   6.752%   $59.1833   $59.18   $59.20   $59.20  
  Purchase #4 $61.55   11.753%   $68.784   $68.78   $68.80   $68.80  
  Purchase #5 $145.93   6.710%   $155.7219   $155.72   $155.70   $155.70  
  Purchase #6 $35.34   4.623%   $36.9738   $36.97   $36.95   $37.00  
  Purchase #7 $203.66   3.860%   $211.5213   $211.52   $211.50   $211.50  
  7 purchase totals = $597.00       $636.1819   $636.17   $636.15   $636.20