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 $128.61   13.258%   $145.6611   $145.66   $145.65   $145.70  
  Purchase #2 $211.39   4.156%   $220.1754   $220.18   $220.20   $220.20  
  Purchase #3 $175.46   10.862%   $194.5185   $194.52   $194.50   $194.50  
  Purchase #4 $155.82   12.689%   $175.592   $175.59   $175.60   $175.60  
  Purchase #5 $150.84   13.627%   $171.395   $171.40   $171.40   $171.40  
  Purchase #6 $68.87   10.511%   $76.1089   $76.11   $76.10   $76.10  
  Purchase #7 $197.82   4.471%   $206.6645   $206.66   $206.65   $206.70  
  7 purchase totals = $1,088.81       $1,190.1154   $1,190.12   $1,190.10   $1,190.20