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 $69.85   6.231%   $74.2024   $74.20   $74.20   $74.20  
  Purchase #2 $174.81   10.789%   $193.6703   $193.67   $193.65   $193.70  
  Purchase #3 $75.53   10.687%   $83.6019   $83.60   $83.60   $83.60  
  Purchase #4 $63.82   9.692%   $70.0054   $70.01   $70.00   $70.00  
  Purchase #5 $109.61   6.844%   $117.1117   $117.11   $117.10   $117.10  
  Purchase #6 $246.59   11.456%   $274.8394   $274.84   $274.85   $274.80  
  Purchase #7 $228.57   5.240%   $240.5471   $240.55   $240.55   $240.50  
  7 purchase totals = $968.78       $1,053.9782   $1,053.98   $1,053.95   $1,053.90