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 $203.68   11.841%   $227.7977   $227.80   $227.80   $227.80  
  Purchase #2 $226.60   9.731%   $248.6504   $248.65   $248.65   $248.70  
  Purchase #3 $45.95   5.693%   $48.5659   $48.57   $48.55   $48.60  
  Purchase #4 $97.72   11.463%   $108.9216   $108.92   $108.90   $108.90  
  Purchase #5 $124.96   5.828%   $132.2427   $132.24   $132.25   $132.20  
  Purchase #6 $75.30   5.176%   $79.1975   $79.20   $79.20   $79.20  
  Purchase #7 $39.57   8.702%   $43.0134   $43.01   $43.00   $43.00  
  7 purchase totals = $813.78       $888.3892   $888.39   $888.35   $888.40