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 $181.66   12.285%   $203.9769   $203.98   $204.00   $204.00  
  Purchase #2 $56.52   7.246%   $60.6154   $60.62   $60.60   $60.60  
  Purchase #3 $48.90   8.421%   $53.0179   $53.02   $53.00   $53.00  
  Purchase #4 $218.88   13.155%   $247.6737   $247.67   $247.65   $247.70  
  Purchase #5 $165.57   3.350%   $171.1166   $171.12   $171.10   $171.10  
  Purchase #6 $220.65   11.149%   $245.2503   $245.25   $245.25   $245.30  
  Purchase #7 $161.93   3.650%   $167.8404   $167.84   $167.85   $167.80  
  7 purchase totals = $1,054.11       $1,149.4912   $1,149.50   $1,149.45   $1,149.50