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 $181.51   4.199%   $189.1316   $189.13   $189.15   $189.10  
  Purchase #2 $155.55   10.369%   $171.679   $171.68   $171.70   $171.70  
  Purchase #3 $41.80   6.208%   $44.3949   $44.39   $44.40   $44.40  
  Purchase #4 $219.72   9.123%   $239.7651   $239.77   $239.75   $239.80  
  Purchase #5 $103.57   6.719%   $110.5289   $110.53   $110.55   $110.50  
  Purchase #6 $19.96   3.517%   $20.662   $20.66   $20.65   $20.70  
  Purchase #7 $102.88   10.743%   $113.9324   $113.93   $113.95   $113.90  
  7 purchase totals = $824.99       $890.0939   $890.09   $890.15   $890.10