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 $86.42   11.220%   $96.1163   $96.12   $96.10   $96.10  
  Purchase #2 $134.82   10.640%   $149.1648   $149.16   $149.15   $149.20  
  Purchase #3 $37.70   5.256%   $39.6815   $39.68   $39.70   $39.70  
  Purchase #4 $207.91   9.490%   $227.6407   $227.64   $227.65   $227.60  
  Purchase #5 $217.25   4.416%   $226.8438   $226.84   $226.85   $226.80  
  Purchase #6 $31.52   11.777%   $35.2321   $35.23   $35.25   $35.20  
  Purchase #7 $159.80   11.608%   $178.3496   $178.35   $178.35   $178.30  
  7 purchase totals = $875.42       $953.0288   $953.02   $953.05   $952.90