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 $176.52   7.376%   $189.5401   $189.54   $189.55   $189.50  
  Purchase #2 $200.97   5.298%   $211.6174   $211.62   $211.60   $211.60  
  Purchase #3 $42.82   6.663%   $45.6731   $45.67   $45.65   $45.70  
  Purchase #4 $222.56   8.874%   $242.31   $242.31   $242.30   $242.30  
  Purchase #5 $38.99   7.420%   $41.8831   $41.88   $41.90   $41.90  
  Purchase #6 $106.85   3.578%   $110.6731   $110.67   $110.65   $110.70  
  Purchase #7 $205.84   3.230%   $212.4886   $212.49   $212.50   $212.50  
  7 purchase totals = $994.55       $1,054.1854   $1,054.18   $1,054.15   $1,054.20