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 $143.54   5.754%   $151.7993   $151.80   $151.80   $151.80  
  Purchase #2 $86.98   5.419%   $91.6934   $91.69   $91.70   $91.70  
  Purchase #3 $31.25   5.632%   $33.01   $33.01   $33.00   $33.00  
  Purchase #4 $202.30   4.705%   $211.8182   $211.82   $211.80   $211.80  
  Purchase #5 $205.84   8.745%   $223.8407   $223.84   $223.85   $223.80  
  Purchase #6 $150.74   13.857%   $171.628   $171.63   $171.65   $171.60  
  Purchase #7 $81.73   12.546%   $91.9838   $91.98   $92.00   $92.00  
  7 purchase totals = $902.38       $975.7734   $975.77   $975.80   $975.70