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 $45.68   4.661%   $47.8091   $47.81   $47.80   $47.80  
  Purchase #2 $233.61   7.823%   $251.8853   $251.89   $251.90   $251.90  
  Purchase #3 $148.35   4.268%   $154.6816   $154.68   $154.70   $154.70  
  Purchase #4 $179.25   12.668%   $201.9574   $201.96   $201.95   $202.00  
  Purchase #5 $108.80   11.689%   $121.5176   $121.52   $121.50   $121.50  
  Purchase #6 $106.95   4.839%   $112.1253   $112.13   $112.15   $112.10  
  Purchase #7 $203.96   8.842%   $221.9941   $221.99   $222.00   $222.00  
  7 purchase totals = $1,026.60       $1,111.9704   $1,111.98   $1,112.00   $1,112.00