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 $134.70   11.838%   $150.6458   $150.65   $150.65   $150.60  
  Purchase #2 $208.84   12.385%   $234.7048   $234.70   $234.70   $234.70  
  Purchase #3 $143.27   8.481%   $155.4207   $155.42   $155.40   $155.40  
  Purchase #4 $137.92   4.819%   $144.5664   $144.57   $144.55   $144.60  
  Purchase #5 $25.53   6.444%   $27.1752   $27.18   $27.20   $27.20  
  Purchase #6 $195.63   5.790%   $206.957   $206.96   $206.95   $207.00  
  Purchase #7 $76.55   5.671%   $80.8912   $80.89   $80.90   $80.90  
  7 purchase totals = $922.44       $1,000.3611   $1,000.37   $1,000.35   $1,000.40