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 $41.73   13.308%   $47.2834   $47.28   $47.30   $47.30  
  Purchase #2 $181.85   11.458%   $202.6864   $202.69   $202.70   $202.70  
  Purchase #3 $43.40   9.498%   $47.5221   $47.52   $47.50   $47.50  
  Purchase #4 $26.94   9.310%   $29.4481   $29.45   $29.45   $29.40  
  Purchase #5 $197.32   4.177%   $205.5621   $205.56   $205.55   $205.60  
  Purchase #6 $45.67   6.251%   $48.5248   $48.52   $48.50   $48.50  
  Purchase #7 $202.84   8.402%   $219.8826   $219.88   $219.90   $219.90  
  7 purchase totals = $739.75       $800.9095   $800.90   $800.90   $800.90