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 $134.66   12.524%   $151.5248   $151.52   $151.50   $151.50  
  Purchase #2 $211.91   6.861%   $226.4491   $226.45   $226.45   $226.40  
  Purchase #3 $127.66   5.631%   $134.8485   $134.85   $134.85   $134.80  
  Purchase #4 $155.64   5.243%   $163.8002   $163.80   $163.80   $163.80  
  Purchase #5 $189.49   6.613%   $202.021   $202.02   $202.00   $202.00  
  Purchase #6 $80.65   12.412%   $90.6603   $90.66   $90.65   $90.70  
  Purchase #7 $77.37   7.688%   $83.3182   $83.32   $83.30   $83.30  
  7 purchase totals = $977.38       $1,052.6221   $1,052.62   $1,052.55   $1,052.50