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 $53.58   13.430%   $60.7758   $60.78   $60.80   $60.80  
  Purchase #2 $70.49   5.248%   $74.1893   $74.19   $74.20   $74.20  
  Purchase #3 $59.95   12.310%   $67.3298   $67.33   $67.35   $67.30  
  Purchase #4 $75.36   5.522%   $79.5214   $79.52   $79.50   $79.50  
  Purchase #5 $181.88   11.698%   $203.1563   $203.16   $203.15   $203.20  
  Purchase #6 $232.46   11.322%   $258.7791   $258.78   $258.80   $258.80  
  Purchase #7 $58.84   9.531%   $64.448   $64.45   $64.45   $64.40  
  7 purchase totals = $732.56       $808.1997   $808.21   $808.25   $808.20