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 $222.25   13.317%   $251.847   $251.85   $251.85   $251.80  
  Purchase #2 $87.25   11.737%   $97.4905   $97.49   $97.50   $97.50  
  Purchase #3 $52.56   3.640%   $54.4732   $54.47   $54.45   $54.50  
  Purchase #4 $42.80   9.106%   $46.6974   $46.70   $46.70   $46.70  
  Purchase #5 $210.50   8.381%   $228.142   $228.14   $228.15   $228.10  
  Purchase #6 $168.67   7.478%   $181.2831   $181.28   $181.30   $181.30  
  Purchase #7 $180.77   12.574%   $203.5   $203.50   $203.50   $203.50  
  7 purchase totals = $964.80       $1,063.4332   $1,063.43   $1,063.45   $1,063.40